Some essential considerations in the design and conduct of non-inferiority trials

Study design approaches for future active-controlled HIV prevention trials

Objectives

Vigorous discussions are ongoing about future efficacy trial designs of candidate human immunodeficiency virus (HIV) prevention interventions. The study design challenges of HIV prevention interventions are considerable given rapid evolution of the prevention landscape and evidence of multiple modalities of highly effective products; future trials will likely be 'active-controlled', i.e., not include a placebo arm. Thus, novel design approaches are needed to accurately assess new interventions against these highly effective active controls.

Methods

To discuss active control design challenges and identify solutions, an initial virtual workshop series was hosted and supported by the International AIDS Enterprise (October 2020-March 2021). Subsequent symposia discussions continue to advance these efforts. As the non-inferiority design is an important conceptual reference design for guiding active control trials, we adopt several of its principles in our proposed design approaches.

Results

We discuss six potential study design approaches for formally evaluating absolute prevention efficacy given data from an active-controlled HIV prevention trial including using data from: 1) a registrational cohort, 2) recency assays, 3) an external trial placebo arm, 4) a biomarker of HIV incidence/exposure, 5) an anti-retroviral drug concentration as a mediator of prevention efficacy, and 6) immune biomarkers as a mediator of prevention efficacy.

Conclusions

Our understanding of these proposed novel approaches to future trial designs remains incomplete and there are many future statistical research needs. Yet, each of these approaches, within the context of an active-controlled trial, have the potential to yield reliable evidence of efficacy for future biomedical interventions.

THE REPORTING QUALITY OF NONINFERIORITY TRIALS USING INTRAVITREAL VASCULAR ENDOTHELIAL GROWTH FACTOR INHIBITORS

PURPOSE

Noninferiority trials (NIFTs) are widely used to study intravitreal vascular endothelial growth factor inhibitors for the treatment of ocular diseases. Thus, this trial design deserves greater attention. We aimed to comprehensively assess the methodological and reporting quality of NIFTs in the field of neovascular ocular diseases.

METHODS

We identified NIFTs using antivascular endothelial growth factor agents published before February 2020 from PubMed and Web of Science. Two independent authors extracted and double-checked predefined elements related to the quality of design and reporting. The characteristics and reporting of NIFTs were described with frequencies and percentages. We summarized important factors that were potentially biased the results of NIFTs and provided point-to-point recommendations.

RESULTS

In total, 34 studies involving 15,190 subjects and 51 pairs of noninferiority comparisons were identified. Areas of concern that could potentially affect the qualities of NIFTs included the absence of justification for the selection of noninferiority margins (61.8%), the use of unusually wide noninferiority margins (26.5%), the lack of outcome confirmation provided by the intention-to-treat and per-protocol analyses (64.7%), the presence of postrandomization exclusions >10% (52.9%), and not declaring the compensatory benefits (35.3%). Moreover, industry-sponsored NIFTs were more likely to draw positive results (P = 0.036).

CONCLUSION

NIFTs of antivascular endothelial growth factor therapies commonly achieved noninferiority of the tested intervention. However, the methodologies and reporting limitations may affect the confidence of the results. Thus, more awareness must be created among investigators for better adherence to guidelines and recommendations while designing, conducting, and reporting on NIFTs.

Evaluating group-sequential non-inferiority clinical trials following interim stopping: The HIV Prevention Trials Network 083 trial

BACKGROUND/AIMS

The HIV Prevention Trials Network 083 trial was a group-sequential non-inferiority trial designed to compare HIV incidence under a novel experimental regimen for HIV prevention, long-acting injectable cabotegravir, with an active-control regimen of daily oral tenofovir disoproxil fumarate/emtricitabine (brand name Truvada). In March of 2020, just as the trial had completed enrollment, the COVID-19 pandemic threatened to prevent trial participants from attending study visits and obtaining study medication, motivating the study team to update the interim monitoring plan. The Data and Safety Monitoring Board subsequently stopped the trial at the first interim review due to strong early evidence of efficacy.

METHODS

Here we describe some unique aspects of the trial's design, monitoring, analysis, and interpretation. We illustrate the importance of computing point estimates, confidence intervals, and p values based on the sampling distribution induced by sequential monitoring.

RESULTS

Accurate analysis, decision-making and interpretation of trial results rely on pre-specification of a stopping boundary, including the scale on which the stopping rule will be implemented, the specific test statistics to be calculated, and how the boundary will be adjusted if the available information fraction at interim review is different from planned. After appropriate adjustment for the sampling distribution and overrun, the HIV Prevention Trials Network 083 trial provided strong evidence that the experimental regimen was superior to the active control.

CONCLUSIONS

For the HIV Prevention Trials Network 083 trial, the difference between corrected inferential statistics and naive results was quite small-as will often be the case-nevertheless, it is appropriate to report and publish the most accurate and unbiased statistical results.

An investigation of the constancy of effect in Cochrane systematic reviews in context with the assumptions for noninferiority trials

When designing a noninferiority (NI) study one of the most important steps is to set the noninferiority (NI) limit. The NI limit is an acceptable loss of efficacy for a new investigative treatment compared to an active control treatment - often standard care. The limit should be a value so small that the loss efficacy is clinically zero. An approach to the setting of a noninferiority limit such that an effect over placebo can be shown through an indirect comparison to placebo-controlled trials where the active control treatment was compared to placebo. In this context, the setting of the NI limit depends on three assumptions: assay sensitivity, bias minimisation, and the constancy assumption. The last assumption of constancy assumes the effect of the active control over placebo is constant. This paper aims to assess the constancy assumption in placebo-controlled trials.

METHODS

236 Cochrane reviews of placebo-controlled trials published in 2015-2016 were collected and used to assess the relation between the placebo, active treatment, and the standardised treatment different (SMD) with the time (year of publication).

RESULTS

The analysis showed that both the size of the study and the treatment effect were associated with year of publication. The three main variables that affect the estimate of any future trial are the estimate from the meta-analysis of previous trials prior to the trial, the year difference in the meta-analysis, and the year of the trial conduction. The regression analysis showed that an increase of one unit in the point estimate of the historical meta-analysis would lead to an increase in the predicted estimate of future trial on the SMD scale by 0.88. This result suggests the final trial results are 12% smaller than that from the meta-analysis of trials until that point.

CONCLUSION

The result of this study indicates that assuming constancy of the treatment difference between the active control and placebo can be questioned. It is therefore important to consider the effect of time in estimating the treatment response if indirect comparisons are being used as the basis of a NI limit.

Borrowing historical information for non-inferiority trials on Covid-19 vaccines

Non-inferiority vaccine trials compare new candidates to active controls that provide clinically significant protection against a disease. Bayesian statistics allows to exploit pre-experimental information available from previous studies to increase precision and reduce costs. Here, historical knowledge is incorporated into the analysis through a power prior that dynamically regulates the degree of information-borrowing. We examine non-inferiority tests based on credible intervals for the unknown effects-difference between two vaccines on the log odds ratio scale, with an application to new Covid-19 vaccines. We explore the frequentist properties of the method and we address the sample size determination problem.

COVID-19 vaccine trials: The potential for "hybrid" analyses

BACKGROUND

Although several COVID-19 vaccines have been found to be effective in rigorous evaluation and have emerging availability in parts of the world, their supply will be inadequate to meet international needs for a considerable period of time. There also will be continued interest in vaccines that are more effective or have improved scalability to facilitate mass vaccination campaigns. Ongoing clinical testing of new vaccines also will be needed as variant strains continue to emerge that may elude some aspects of immunity induced by current vaccines. Randomized clinical trials meaningfully enhance the efficiency and reliability of such clinical testing. In clinical settings with limited or no access to known effective vaccines, placebo-controlled randomized trials of new vaccines remain a preferred approach to maximize the reliability, efficiency and interpretability of results. When emerging availability of licensed vaccines makes it no longer possible to use a placebo control, randomized active comparator non-inferiority trials may enable reliable insights.

METHODS

In this article, "hybrid" methods are proposed to address settings where, during the conduct of a placebo-controlled trial, a judgment is made to replace the placebo arm by a licensed COVID-19 vaccine due to emerging availability of effective vaccines in regions participating in that trial. These hybrid methods are based on proposed statistics that aggregate evidence to formally test as well as to estimate the efficacy of the experimental vaccine, by combining placebo-controlled data during the first period of trial conduct with active-controlled data during the second period.

RESULTS

Application of the proposed methods is illustrated in two important scenarios where the active control vaccine would become available in regions engaging in the experimental vaccine's placebo-controlled trial: in the first, the active comparator's vaccine efficacy would have been established to be 50%-70% for the 4- to 6-month duration of follow-up of its placebo-controlled trial; in the second, the active comparator's vaccine efficacy would have been established to be 90%-95% during that duration. These two scenarios approximate what has been seen with adenovirus vaccines or mRNA vaccines, respectively, assuming the early estimates of vaccine efficacy for those vaccines would hold over longer-term follow-up.

CONCLUSION

The proposed hybrid methods could readily play an important role in the near future in the design, conduct and analysis of randomized clinical trials performed to address the need for multiple additional vaccines reliably established to be safe and have worthwhile efficacy in reducing the risk of symptomatic disease from SARS-CoV-2 infections.

Induction chemotherapy with lobaplatin and fluorouracil versus cisplatin and fluorouracil followed by chemoradiotherapy in patients with stage III-IVB nasopharyngeal carcinoma: an open-label, non-inferiority, randomised, controlled, phase 3 trial

BACKGROUND

Cisplatin-based induction chemotherapy plus concurrent chemoradiotherapy in the treatment of patients with locoregionally advanced nasopharyngeal carcinoma has been recommended in the National Comprehensive Cancer Network Guidelines. However, cisplatin is associated with poor patient compliance and has notable side-effects. Lobaplatin, a third-generation platinum drug, has shown promising antitumour activity against several malignancies with less toxicity. In this study, we aimed to evaluate the efficacy of lobaplatin-based induction chemotherapy plus concurrent chemoradiotherapy over a cisplatin-based regimen in patients with locoregional, advanced nasopharyngeal carcinoma.

METHODS

In this open-label, non-inferiority, randomised, controlled, phase 3 trial done at five hospitals in China, patients aged 18-60 years with previously untreated, non-keratinising stage III-IVB nasopharyngeal carcinoma; Karnofsky performance-status score of at least 70; and adequate haematological, renal, and hepatic function were randomly assigned (1:1) to receive intravenously either lobaplatin-based (lobaplatin 30 mg/m² on days 1 and 22, and fluorouracil 800 mg/m² on days 1-5 and 22-26 for two cycles) or cisplatin-based (cisplatin 100 mg/m² on days 1 and 22, and fluorouracil 800 mg/m² on days 1-5 and 22-26 for two cycles) induction chemotherapy, followed by concurrent lobaplatin-based (two cycles of intravenous lobaplatin 30 mg/m² every 3 weeks plus intensity-modulated radiotherapy) or cisplatin-based (two cycles of intravenous cisplatin 100 mg/m² every 3 weeks plus intensity-modulated radiotherapy) chemoradiotherapy. Total radiation doses of 68-70 Gy (for the sum of the volumes of the primary tumour and enlarged retropharyngeal nodes), 62-68 Gy (for the volume of clinically involved gross cervical lymph nodes), 60 Gy (for the high-risk target volume), and 54 Gy (for the low-risk target volume), were administered in 30-32 fractions, 5 days per week. Randomisation was done centrally at the clinical trial centre of Sun Yat-sen University Cancer Centre by means of computer-generated random number allocation with a block design (block size of four) stratified according to disease stage and treatment centre. Treatment assignment was known to both clinicians and patients. The primary endpoint was 5-year progression-free survival, analysed in both the intention-to-treat and per-protocol populations. If the upper limit of the 95% CI for the difference in 5-year progression-free survival between the lobaplatin-based and cisplatin-based groups did not exceed 10%, non-inferiority was met. Adverse events were analysed in all patients who received at least one cycle of induction chemotherapy. This trial is registered with the Chinese Clinical Trial Registry, ChiCTR-TRC-13003285 and is closed.

FINDINGS

From June 7, 2013, to June 16, 2015, 515 patients were assessed for eligibility and 502 patients were enrolled: 252 were randomly assigned to the lobaplatin-based group and 250 to the cisplatin-based group. After a median follow-up of 75·3 months (IQR 69·9-81·1) in the intention-to-treat population, 5-year progression-free survival was 75·0% (95% CI 69·7-80·3) in the lobaplatin-based group and 75·5% (70·0 to 81·0) in the cisplatin-based group (hazard ratio [HR] 0·98, 95% CI 0·69-1·39; log-rank p=0·92), with a difference of 0·5% (95% CI -7·1 to 8·1; p_{non-inferiority}=0·0070). In the per-protocol population, the 5-year progression-free survival was 74·8% (95% CI 69·3 to 80·3) in the lobaplatin-based group and 76·4% (70·9 to 81·9) in the cisplatin-based group (HR 1·04, 95% CI 0·73 to 1·49; log-rank p=0·83), with a difference of 1·6% (-6·1 to 9·3; p_{non-inferiority}=0·016). 63 (25%) of 252 patients in the lobaplatin-based group and 63 (25%) of 250 patients in the cisplatin-based group had a progression-free survival event in the intention-to-treat population; 62 (25%) of 246 patients in the lobaplatin-based group and 58 (25%) of 237 patients in the cisplatin-based group had a progression-free survival event in the per-protocol population. The most common grade 3-4 adverse events were mucositis (102 [41%] of 252 in the lobaplatin-based group vs 99 [40%] of 249 in the cisplatin-based group), leucopenia (39 [16%] vs 56 [23%]), and neutropenia (25 [10%] vs 59 [24%]). No treatment-related deaths were reported.

INTERPRETATION

Lobaplatin-based induction chemotherapy plus concurrent chemoradiotherapy resulted in non-inferior survival and fewer toxic effects than cisplatin-based therapy. The results of our trial indicate that lobaplatin-based induction chemotherapy plus concurrent chemoradiotherapy might be a promising alternative regimen to cisplatin-based treatment in patients with locoregional, advanced nasopharyngeal carcinoma.

FUNDING

National Science and Technology Pillar Program, International Cooperation Project of Science and Technology Program of Guangdong Province, Planned Science and Technology Project of Guangdong Province, and Cultivation Foundation for the Junior Teachers at Sun Yat-sen University.

TRANSLATION

For the Chinese translation of the abstract see Supplementary Materials section.

A systematic review of noninferiority margins in oncology clinical trials

Aim: A systematic literature review was conducted to identify and characterize noninferiority margins for relevant end points in oncology clinical trials. Materials & methods: Randomized, controlled, noninferiority trials of patients with cancer were identified in PubMed and Embase. Results: Of 2284 publications identified, 285 oncology noninferiority clinical trials were analyzed. The median noninferiority margin was a hazard ratio of 1.29 (mean: 1.32; range: 1.05-2.05) for studies that reported time-to-event end points (n = 192). The median noninferiority margin was 13.0% (mean: 12.7%; range: 5.0-20.0%) for studies that reported response end points as absolute rate differences (n = 31). Conclusion: Although there was consistency in the noninferiority margins' scale, variability was evident in noninferiority margins across trials. Increased transparency may improve consistency in noninferiority margin application in oncology clinical trials.

Adaptive disclosure, a combat-specific PTSD treatment, versus cognitive-processing therapy, in deployed marines and sailors: A randomized controlled non-inferiority trial

Adaptive Disclosure (AD) is a new emotion-focused psychotherapy for combat-related PTSD. As a second step in the evaluation process, we conducted a non-inferiority (NI) trial of AD, relative to Cognitive Processing Therapy - Cognitive Therapy version (CPT-C), an established first-line psychotherapy. Participants were 122 U.S. Marines and Sailors. The primary endpoint was PTSD symptom severity change from pre- to posttreatment, using the Clinician Administered PTSD Scale for DSM-IV. Secondary endpoints were depression (Patient Health Questionnaire-9; PHQ-9) and functioning (Veterans Rand Health Survey-12; VR-12). For cases with complete data, the mean difference in CAPS-IV change scores was 0.33 and the confidence interval (CI) did not include the predefined NI margin (95% CI =-10.10, 9.44). The mean difference in PHQ-9 change scores was -1.01 and the CI did not include the predefined margin (95% CI = -3.31, 1.28), as was the case for the VR-12 Physical Component and VR-12 Mental Component subscale scores (0.27; 95% CI = -4.50, 3.95, and -2.10; 95% CI = -7.03, 2.83, respectively). A series of intent-to-treat sensitivity analyses confirmed these results. The differential effect size for CAPS-IV was d = 0.01 (nonsignificant). As predicted, Adaptive Disclosure was found to be no less effective than a first-line psychotherapy.

COVID-19 vaccine trials: The use of active controls and non-inferiority studies

Background:

Recently emerging results from a few placebo-controlled randomized trials of COVID-19 vaccines revealed estimates of 62%–95% relative reductions in risk of virologically confirmed symptomatic COVID-19 disease, over approximately 2-month average follow-up period. Additional safe and effective COVID-19 vaccines are needed in a timely manner to adequately address the pandemic on an international scale. Such safe and effective vaccines would be especially appealing for international deployment if they also have favorable stability, supply, and potential for implementation in mass vaccination campaigns. Randomized trials provide particularly reliable insights about vaccine efficacy and safety. While enhanced efficiency and interpretability can be obtained from placebo-controlled trials, in settings where their conduct is no longer possible, randomized non-inferiority trials may enable obtaining reliable evaluations of experimental vaccines through direct comparison with active comparator vaccines established to have worthwhile efficacy.

Methods:

The usual objective of non-inferiority trials is to reliably assess whether the efficacy of an experimental vaccine is not unacceptably worse than that of an active control vaccine previously established to be effective, likely in a placebo-controlled trial. This is formally achieved by ruling out a non-inferiority margin identified to be the minimum threshold for what would constitute an unacceptable loss of efficacy. This article not only investigates non-inferiority margins, denoted by δ, that address the usual objective of determining whether the experimental vaccine is “at least similarly effective to” the active comparator vaccine in the non-inferiority trial, but also develops non-inferiority margins, denoted by δ_o, intended to address the worldwide need for multiple safe and effective vaccines by satisfying the less stringent requirement that the experimental vaccine be “at least similarly effective to” an active comparator vaccine having efficacy that satisfies the widely accepted World Health Organization–Food and Drug Administration criteria for “worthwhile” vaccine efficacy.

Results:

Using the margin δ enables non-inferiority trials to reliably evaluate experimental vaccines that truly are similarly effective to an active comparator vaccine having any level of “worthwhile” efficacy. When active comparator vaccines have efficacy in the range of 50%–70%, non-inferiority trials designed to use the margin δ_o have appealing properties, especially for experimental vaccines having true efficacy of approximately 60%.

Conclusion:

Non-inferiority trials using the proposed margins may enable reliable randomized evaluations of efficacy and safety of experimental COVID-19 vaccines. Such trials often require approximately two- to three-fold the person-years follow-up than a placebo-controlled trial. This could be achieved, without substantive increases in sample size, by increasing the average duration of follow-up from 2 months to approximately 4–6 months, assuming efficacy of the active comparator vaccine has been reliably evaluated over that longer duration.

A Bayesian averted infection framework for PrEP trials with low numbers of HIV infections: application to the results of the DISCOVER trial

Trials of candidate agents for HIV pre-exposure prophylaxis (PrEP) might randomly assign participants to be given a new PrEP agent or oral coformulated tenofovir disoproxil fumarate plus emtricitabine. This design presents unique challenges in interpretation. First, with two active arms, HIV incidence might be low. Second, the effectiveness of tenofovir disoproxil fumarate plus emtricitabine varies across populations; thus, similar HIV incidence between groups could be consistent with a wide range of effectiveness for the new PrEP. We propose a two-part approach to trial results. First, we use Bayesian methods to incorporate assumptions about the background incidence of HIV in the trial in the absence of PrEP, possibly augmented by external data. On the basis of the estimated background incidence, we estimate and compare the number of averted (or prevented) HIV infections in each of the two trial groups, calculating the averted infections ratio. We apply these methods to a completed trial of tenofovir alafenamide plus emtricitabine for PrEP. Our framework shows that leveraging external information to estimate averted infections and the averted infections ratio enhances the efficiency and interpretation of active-controlled PrEP trials.

Comparison of alternative approaches for difference, noninferiority, and equivalence testing of normal percentiles

Background

Percentiles are widely used in scientific research for determining the comparative magnitude and reference limit of quantitative measurements. The investigations for point and interval estimation of normal percentiles are well documented in the literature. However, the corresponding statistical tests of hypothesis have received relatively little attention.

Methods

To facilitate data analysis and design planning of percentile study, this paper aims to present hypothesis testing procedures and associated power functions for assessing the difference, noninferiority, and equivalence of normal percentiles.

Results

Numerical illustrations about drug dissolution are provided to demonstrate the usefulness of the suggested exact approaches and the deficiency of approximate methods.

Conclusions

The exact approaches are superior to the approximate methods on the basis of control of Type I errors. Computer algorithms are constructed to implement the recommended test procedures and sample size calculations for percentile analysis.

Trial Design Challenges and Approaches for Precision Oncology in Rare Tumors: Experiences of the Children's Oncology Group

In the United States, cancer remains the leading cause of disease-related death in children. Although survival from any pediatric cancer has improved dramatically during past decades, a number of cancers continue to yield dismal prognoses, which has motivated the continued study of novel therapeutic strategies. Furthermore, even patients cured of pediatric cancer often experience severe adverse effects of treatment and other long-term health implications, such as cardiotoxicity or loss of fertility. For these patients, improved risk stratification to identify those who could safely receive alternate or less-intensive therapy without affecting prognosis is a key objective. Fortunately, pediatric cancers are rare overall, but even among patients with the same narrow cancer type, there is often broad heterogeneity in terms of prognosis, molecular features or pathology, current treatment strategies, and scientific objectives. As a result, the design of clinical trials in the pediatric cancer setting is challenged by a number of practical issues that must be addressed to ensure trial feasibility for this vulnerable group of patients. In this review, we discuss some of the unique trial design considerations often encountered in any rare tumor setting through the lens of our experiences as faculty statisticians for the Children's Oncology Group, the largest organization in the world dedicated exclusively to pediatric cancer research and clinical trials. These topics include risk stratification within individual trials, relaxation of trial operating characteristics and parameters, use of historical controls, and address of noninferiority-type objectives in small cohorts. We review each in terms of practical motivation, present challenges, and potential solutions described in the literature and implemented in selected example trials from the Children's Oncology Group.

Mosaic effectiveness: measuring the impact of novel PrEP methods

Various ongoing trials seek to evaluate long-acting pre-exposure prophylaxis (PrEP) agents by showing that they are non-inferior to daily oral tenofovir disoproxil fumarate and emtricitabine. Trials comparing oral PrEP to new methods examine effectiveness in a setting where only one or the other is provided; however, a new product will probably be delivered in a context where oral PrEP is also available. The effectiveness of a new PrEP product is best measured by its potential effect in a context that also includes oral tenofovir disoproxil fumarate and emtricitabine as an option. We offer an alternative standard for long-acting products-a measure of the effectiveness of the new product in addition to oral tenofovir disoproxil fumarate and emtricitabine as compared with oral PrEP alone. We term this measure mosaic effectiveness. We illustrate scenarios where a novel product can fail to show non-inferiority but show substantial mosaic effectiveness, thus implying the public health value of the novel product even if it is less effective than oral PrEP. Regulatory standards should consider mosaic effectiveness, not just comparative effectiveness. We assert that measurements that combine rigor with public health relevance can accelerate progress against the HIV epidemic.

A reproducibility probability-based bias-adjustment approach on the specification of non-inferiority margin using historical data

The effect of reference treatment over placebo, known as M1, is essential in the development of non-inferiority margin. We proposed a M1 adjustment approach to reduce the selection bias for collected data of historical trials. A quantitative illustration of selection bias of historical data is also defined. Simulation study shows that the proposed approaches would significantly reduce the bias when the proportion of positive studies in historical data is noticeably larger than the power of studies include in historical data. When historical data are constituted by only positive studies, the performance of the proposed method is also appreciable. However, when the proportion of positive studies is close to the power of studies included or the number of studies included is too small, the performance of the proposed approach may not be reliable. A real-data application is also presented. The proposed bias-adjustment approach is a reasonable method to reduce the over-estimate of effect size in the specification of non-inferiority margin. It could also be applied in most non-inferiority margin specification methods or be cooperate used with other bias-adjustment approaches.

Taking stock of the present and looking ahead: envisioning challenges in the design of future HIV prevention efficacy trials

Despite the recent success of antiretrovirals for HIV prevention, additional, more effective, or more acceptable biomedical interventions will ultimately be needed to end the HIV epidemic. Designing clinical trials to evaluate the efficacy of new products that reduce HIV infection risk is challenging because of the existence of highly effective interventions to prevent HIV. However, the implementation of these interventions is uneven, and the fact that multiple HIV prevention efficacy trials are currently evaluating new products means the field confronts uncertainty in the emerging standard of prevention. In this Viewpoint, we take stock of the current state of HIV prevention, and subsequently discuss the key challenges in designing future trials to evaluate the next generation of HIV prevention products. We also highlight gaps in the knowledge base that need to be addressed to advance the design of research. Future trials are tenable, even in the context of existing and effective interventions, and should involve careful statistical approaches and multidisciplinary collaborative design.

Optimal contrast analysis with heterogeneous variances and budget concerns

The omnibus test is commonly applied to evaluate the overall disparity between group means in ANOVA. Alternatively, linear contrasts are more informative in detecting specific pattern of mean differences that cannot be obtained via the omnibus test. This article concerns power and sample size calculations for contrast analysis with heterogeneous variances and budget concerns. Optimal allocation procedures for the Welch-Satterthwaite tests of standardized and unstandardized contrasts are presented to minimize the total sample size with the designated ratios, to meet a desirable power level for the least cost, and to attain the maximum power performance under a fixed cost. Currently available methods rely exclusively on simple allocation formula and direct rounding rule. The proposed allocation strategies combine the computing techniques of nonlinear optimization search and iterative screening process. Numerical assessments of a randomized control trial for the overcoming depression on the Internet are conducted to demonstrate and confirm that the approximate procedures do not guarantee optimal solution. The suggested approaches extend and outperform the existing findings in methodological soundness and overall performance. The corresponding computer algorithms are developed to implement the recommended power and sample size calculations for optimal contrast analysis.

Advancing Novel PrEP Products - Alternatives to Non-Inferiority

With the scale-up of HIV pre-exposure prophylaxis (PrEP) with tenofovir (TDF) with or without emtricitabine (FTC), we have entered an era of highly effective HIV prevention with a growing pipeline of potential products to be studied. These studies are likely to be randomized trials with an oral TDF/FTC control arm. These studies require comparison of incident infections and can be time and resource intensive. Conventional approaches for design and analysis active controlled trial can lead to very large sample sizes. We demonstrate the important of assumptions about background infections for interpreting trial results and suggest alternative criteria for demonstrating the efficacy and effectiveness of potential PrEP agents.

Designing & Conducting Trials To Reliably Evaluate HIV Prevention Interventions

While much has been achieved, much remains to be accomplished in the science of preventing the spread of HIV infection. Clinical trials that are properly designed, conducted and analyzed are of integral importance in the pursuit of reliable insights about HIV prevention. As we build on previous scientific breakthroughs, there will be an increasing need for clinical trials to be designed to efficiently achieve insights without compromising their reliability and generalizability. Key design features should continue to include: 1) the use of randomization and evidence-based controls, 2) specifying the use of intention-to-treat analyses to preserve the integrity of randomization and to increase interpretability of results, 3) obtaining direct assessments of effects on clinical endpoints such as the risk of HIV infection, 4) using either superiority designs or non-inferiority designs with rigorous non-inferiority margins, and 5) enhancing generalizability through the choice of a relative risk rather than risk difference metric. When interventions have complementary and potentially synergistic effects, factorial designs should be considered to increase efficiency as well as to obtain clinically important insights about interaction and the contribution of component interventions to the efficacy and safety of combination regimens. Key trial conduct issues include timely enrollment of participants at high HIV risk recruited from populations with high viral burden, obtaining 'best real-world achievable' levels of adherence to the interventions being assessed and ensuring high levels of retention. High quality of trial conduct occurs through active rather than passive monitoring, using pre-specified targeted levels of performance with defined methods to achieve those targets. During trial conduct, active monitoring of the performance standards not only holds the trial leaders accountable but also can assist in the development and implementation of creative alternative approaches to increase the quality of trial conduct. Designing, conducting and analyzing HIV prevention trials with the quality needed to obtain reliable insights is an ethical as well as scientific imperative.

Ongoing Vaccine and Monoclonal Antibody HIV Prevention Efficacy Trials and Considerations for Sequel Efficacy Trial Designs

Four randomized placebo-controlled efficacy trials of a candidate vaccine or passively infused monoclonal antibody for prevention of HIV-1 infection are underway (HVTN 702 in South African men and women; HVTN 705 in sub-Saharan African women; HVTN 703/HPTN 081 in sub-Saharan African women; HVTN 704/HPTN 085 in U.S., Peruvian, Brazilian, and Swiss men or transgender persons who have sex with men). Several challenges are posed to the optimal design of the sequel efficacy trials, including: (1) how to account for the evolving mosaic of effective prevention interventions that may be part of the trial design or standard of prevention; (2) how to define viable and optimal sequel trial designs depending on the primary efficacy results and secondary "correlates of protection" results of each of the ongoing trials; and (3) how to define the primary objective of sequel efficacy trials if HIV-1 incidence is expected to be very low in all study arms such that a standard trial design has a steep opportunity cost. After summarizing the ongoing trials, I discuss statistical science considerations for sequel efficacy trial designs, both generally and specifically to each trial listed above. One conclusion is that the results of "correlates of protection" analyses, which ascertain how different host immunological markers and HIV-1 viral features impact HIV-1 risk and prevention efficacy, have an important influence on sequel trial design. This influence is especially relevant for the monoclonal antibody trials because of the focused pre-trial hypothesis that potency and coverage of serum neutralization constitutes a surrogate endpoint for HIV-1 infection. Another conclusion is that while assessing prevention efficacy against a counterfactual placebo group is fraught with risks for bias, such analysis is nonetheless important and study designs coupled with analysis methods should be developed to optimize such inferences. I draw a parallel with non-inferiority designs, which are fraught with risks given the necessity of making unverifiable assumptions for interpreting results, but nevertheless have been accepted when a superiority design is not possible and a rigorous/conservative non-inferiority margin is used. In a similar way, counterfactual placebo group efficacy analysis should use rigorous/conservative inference techniques that formally build in a rigorous/conservative margin to potential biases that could occur due to departures from unverifiable assumptions. Because reliability of this approach would require new techniques for verifying that the study cohort experienced substantial exposure to HIV-1, currently it may be appropriate as a secondary objective but not as a primary objective.

Missing data handling in non-inferiority and equivalence trials: A systematic review

BACKGROUND

Non-inferiority (NI) and equivalence clinical trials test whether a new treatment is therapeutically no worse than, or equivalent to, an existing standard of care. Missing data in clinical trials have been shown to reduce statistical power and potentially bias estimates of effect size; however, in NI and equivalence trials, they present additional issues. For instance, they may decrease sensitivity to differences between treatment groups and bias toward the alternative hypothesis of NI (or equivalence).

AIMS

Our primary aim was to review the extent of and methods for handling missing data (model-based methods, single imputation, multiple imputation, complete case), the analysis sets used (Intention-To-Treat, Per-Protocol, or both), and whether sensitivity analyses were used to explore departures from assumptions about the missing data.

METHODS

We conducted a systematic review of NI and equivalence trials published between May 2015 and April 2016 by searching the PubMed database. Articles were reviewed primarily by 2 reviewers, with 6 articles reviewed by both reviewers to establish consensus.

RESULTS

Of 109 selected articles, 93% reported some missing data in the primary outcome. Among those, 50% reported complete case analysis, and 28% reported single imputation approaches for handling missing data. Only 32% reported conducting analyses of both intention-to-treat and per-protocol populations. Only 11% conducted any sensitivity analyses to test assumptions with respect to missing data.

CONCLUSION

Missing data are common in NI and equivalence trials, and they are often handled by methods which may bias estimates and lead to incorrect conclusions.

Consistency ensured test strategies for supportive evidence of treatment efficacy in noninferiority clinical trials

Noninferiority (NI) clinical trials are designed to demonstrate that a new treatment is not unacceptably worse than an active control on a clinically meaningful endpoint. While such an endpoint can be of any type, the focus of this manuscript is on the binary-type endpoint. Examples of this endpoint can be clinical cure endpoint for patients with bacterial diseases or based on a pre-specified virological threshold for viral diseases. However, in addition to assessing such a binary endpoint for the NI comparison, the trial may also evaluate a second clinically relevant endpoint for providing additional support to the evidence of the designated primary endpoint. Specifically, if the trial is successful in demonstrating statistical significance on the first endpoint, then observing at least a positive trend in efficacy on the second endpoint may provide additional supportive evidence of efficacy. The second endpoint can be a time-to-event type endpoint, such as time-to-symptom resolution (TSR) or time to all-cause mortality for infectious disease trials, time-to-wound closure for wound healing trials, or other endpoints. We propose two consistency ensured test strategies for the two hypotheses of a trial, one associated with the binary endpoint and the other with the second endpoint, both with the objective of drawing inference regarding the efficacy of the new treatment based on findings from testing the two hypotheses. A key feature of these test strategies is that basically it does not require multiplicity adjustment of the significance levels. We conclude with general discussion of the testing methods and possible applications to unmet medical need trials.

Defining the noninferiority margin and analysing noninferiority: An overview

Noninferiority trials are used to assess whether the effect of a new drug is not worse than an active comparator by more than a noninferiority margin. If the difference between the new drug and the active comparator does not exceed this prespecified margin, noninferiority can be concluded. This margin must be specified based on clinical and statistical reasoning; however, it is considered as one of the most challenging steps in the design of noninferiority trials. Regulators recommend that the margin should be defined based on the historical evidence of the active comparator (the latter is often the well-established standard treatment of the disease), which can be performed by different approaches. There are several factors and assumptions that need to be accounted for during the process of defining the margin and during the analysis of noninferiority. Three methods are commonly used to analyse noninferiority trials: the fixed-margin method; the point-estimate method; and the synthesis method. This article provides an overview of analysing noninferiority and choosing the noninferiority margin.

Non-inferiority versus superiority drug claims: the (not so) subtle distinction

BACKGROUND

Current regulatory guidance and practice of non-inferiority trials are asymmetric in favor of the test treatment (Test) over the reference treatment (Control). These trials are designed to compare the relative efficacy of Test to Control by reference to a clinically important margin, M.

MAIN TEXT

Non-inferiority trials allow for the conclusion of: (a) non-inferiority of Test to Control if Test is slightly worse than Control but by no more than M; and (b) superiority if Test is slightly better than Control even if it is by less than M. From Control's perspective, (b) should lead to a conclusion of non-inferiority of Control to Test. The logical interpretation ought to be that, while Test is statistically better, it is not clinically superior to Control (since Control should be able to claim non-inferiority to Test). This article makes a distinction between statistical and clinical significance, providing for symmetry in the interpretation of results. Statistical superiority and clinical superiority are achieved, respectively, when the null and the non-inferiority margins are exceeded. We discuss a similar modification to placebo-controlled trials.

CONCLUSION

Rules for interpretation should not favor one treatment over another. Claims of statistical or clinical superiority should depend on whether or not the null margin or the clinically relevant margin is exceeded.

Adaptive Designs for Non-inferiority Trials with Multiple Experimental Treatments

The increase in the popularity of non-inferiority clinical trials represents the increasing need to search for substitutes for some reference (standard) treatments. A new treatment would be preferred to the standard treatment if the benefits of adopting it outweigh a possible clinically insignificant reduction in treatment efficacy (non-inferiority margin). Statistical procedures have recently been developed for treatment comparisons in non-inferiority clinical trials that have multiple experimental (new) treatments. An ethical concern for non-inferiority trials is that some patients undergo the less effective treatments; this problem is more serious when multiple experimental treatments are included in a balanced trial in which the sample sizes are the same for all experimental treatments. With the aim of giving fewer patients the inferior treatments, we propose a response-adaptive treatment allocation scheme that is based on the doubly adaptive biased coin design. The proposed adaptive design is also shown to be superior to the balanced design in terms of testing power.

Testing of non-inferiority and superiority for three-arm clinical studies with multiple experimental treatments

The purpose of a non-inferiority trial is to assert the efficacy of an experimental treatment compared with a reference treatment by showing that the experimental treatment retains a substantial proportion of the efficacy of the reference treatment. Statistical methods have been developed to test multiple experimental treatments in three-arm non-inferiority trials. In this paper, we report the development of procedures that simultaneously test the non-inferiority and the superiority of experimental treatments after the assay sensitivity has been established. The advantage of the proposed test procedures is the additional ability to identify superior treatments while retaining an non-inferiority testing power comparable to that of existing testing procedures. Single-step and stepwise procedures are derived and then compared with each other to determine their relative testing power and testing error in a simulation study. Finally, the suggested procedures are illustrated with two clinical examples.

Virtual reality by mobile smartphone: improving child pedestrian safety

BACKGROUND

Pedestrian injuries are a leading cause of paediatric injury. Effective, practical and cost-efficient behavioural interventions to teach young children street crossing skills are needed. They must be empirically supported and theoretically based. Virtual reality (VR) offers promise to fill this need and teach child pedestrian safety skills for several reasons, including: (A) repeated unsupervised practice without risk of injury, (B) automated feedback on crossing success or failure, (C) tailoring to child skill levels: (D) appealing and fun training environment, and (E) most recently given technological advances, potential for broad dissemination using mobile smartphone technology.

OBJECTIVES AND METHODS

Extending previous work, we will evaluate delivery of an immersive pedestrian VR using mobile smartphones and the Google Cardboard platform, technology enabling standard smartphones to function as immersive VR delivery systems. We will overcome limitations of previous research suggesting children learnt some pedestrian skills after six VR training sessions but did not master adult-level pedestrian skills by implementing a randomised non-inferiority trial with two equal-sized groups of children ages 7-8 years (total N=498). All children will complete baseline, postintervention and 6-month follow-up assessments of pedestrian safety and up to 25 30-min pedestrian safety training trials until they reach adult levels of functioning. Half the children will be randomly assigned to train in Google Cardboard and the other half in a semi-immersive kiosk VR. Analysis of Covariance (ANCOVA) models will assess primary outcomes.

DISCUSSION

If results are as hypothesised, mobile smartphones offer substantial potential to overcome barriers of dissemination and implementation and deliver pedestrian safety training to children worldwide.

Detecting and accounting for violations of the constancy assumption in non-inferiority clinical trials

Randomized, placebo-controlled clinical trials are the gold standard for evaluating a novel therapeutic agent. In some instances, it may not be considered ethical or desirable to complete a placebo-controlled clinical trial and, instead, the placebo is replaced by an active comparator with the objective of showing either superiority or non-inferiority to the active comparator. In a non-inferiority trial, the experimental treatment is considered non-inferior if it retains a pre-specified proportion of the effect of the active comparator as represented by the non-inferiority margin. A key assumption required for valid inference in the non-inferiority setting is the constancy assumption, which requires that the effect of the active comparator in the non-inferiority trial is consistent with the effect that was observed in previous trials. It has been shown that violations of the constancy assumption can result in a dramatic increase in the rate of incorrectly concluding non-inferiority in the presence of ineffective or even harmful treatment. In this paper, we illustrate how Bayesian hierarchical modeling can be used to facilitate multi-source smoothing of the data from the current trial with the data from historical studies, enabling direct probabilistic evaluation of the constancy assumption. We then show how this result can be used to adapt the non-inferiority margin when the constancy assumption is violated and present simulation results illustrating that our method controls the type-I error rate when the constancy assumption is violated, while retaining the power of the standard approach when the constancy assumption holds. We illustrate our adaptive procedure using a non-inferiority trial of raltegravir, an antiretroviral drug for the treatment of HIV.

Survival and Toxicity After Cisplatin Plus Etoposide Versus Carboplatin Plus Etoposide for Extensive-Stage Small-Cell Lung Cancer in Elderly Patients

PURPOSE

Elderly patients with cancer are under-represented in clinical trials and risk greater toxicity from chemotherapy. These patients and their physicians need better evidence to decide among guideline-recommended regimens. We test whether patients with extensive-stage small-cell lung cancer (ES SCLC) have noninferior survival and less hospital-based health care after carboplatin/etoposide compared with cisplatin/etoposide.

METHODS

We analyzed SEER-Medicare data for beneficiaries with ES SCLC diagnosed at age 67 years and older between 1995 and 2009. Among patients treated with first-line chemotherapy in the ambulatory setting, 831 received cisplatin/etoposide and 2,846 received carboplatin/etoposide. Propensity score matching (2:1 ratio) yielded 778 cisplatin/etoposide and 1,502 carboplatin/etoposide patients.

RESULTS

Survival was nearly identical in the two groups: 35.7 weeks for cisplatin/etoposide and 35.9 weeks for carboplatin/etoposide. The hazard ratio of 1 (95% CI, 0.91 to 1.09) excluded our prespecified threshold, indicating noninferiority. Mortality at 6 months was indistinguishable: 35% for cisplatin/etoposide and 34% for carboplatin/etoposide. After carboplatin/etoposide, patients were less likely to be admitted to a hospital (80% v 86%, P < .001) and had fewer hospitalizations (median 1 v 2, odds ratio 0.76, 95% CI, 0.65 to 0.9), ED visits (median 1 v 2, odds ratio 0.82, 95% CI, 0.7 to 0.96), and ICU stays (median 0 v 0, odds ratio 0.82, 95% CI, 0.69 to 0.99).

CONCLUSION

First-line carboplatin/etoposide is associated with similar survival and less subsequent hospital-based health care use than cisplatin/etoposide among elderly patients with ES SCLC treated in ambulatory settings.

Effectiveness of Transdiagnostic Cognitive Behaviour Therapy for Anxiety and Depression in Adults: A Systematic Review and Meta-analysis

Background: Transdiagnostic Cognitive Behaviour Therapy (CBT) seeks to identify core cognitive-behavioural processes hypothesized to be important across a range of disorders and to develop a treatment that targets these. This contrasts with standard CBT approaches that are disorder-specific. Proponents of transdiagnostic CBT suggest that it may offer advantages over disorder-specific CBT, but little is known about the effectiveness of this approach. Aims: The review aimed to summarize trial-based clinical and cost-effectiveness data on transdiagnostic CBT for anxiety and depression. Method: A systematic review of electronic databases, including peer-reviewed and grey literature sources, was conducted (n = 1167 unique citations). Results: Eight trials were eligible for inclusion in the review. There was evidence of an effect for transdiagnostic CBT when compared to a control condition. There were no differences between transdiagnostic CBT and active treatments in two studies. We found no evidence of cost-effectiveness data. Conclusions: Quality assessment of the primary studies indicated a number of methodological concerns that may serve to inflate the observed effects of transdiagnostic approaches. Although there are positive signs of the value of transdiagnostic CBT, there is as yet insufficient evidence to recommend its use in place of disorder-specific CBT.

On robustness of noninferiority clinical trial designs against bias, variability, and nonconstancy

The regulatory guidelines on noninferiority (NI) trials emphasize constancy not only in the treatment effect over time but also in the trial design, clinical practice, and quality of the trial conduct and execution. In practice, the constancy assumption is generally impossible to justify; often, there are clear reasons to expect a loss of efficacy over time. There are also concerns about the inherent and publication bias in the historical data, and various sources of selection bias in the NI trial design. Thus, a conservative NI margin is often considered. However, different NI margin approaches are largely evaluated under the assumption of constancy and absence of bias, and therefore, controversies arise and are unresolved on the necessary degree of conservativeness. We develop a framework to quantify the robustness of any NI margin approach against inherent and publication bias in historical data, selection bias in trial design, and nonconstancy in reference effects. We introduce a consistency principle to address variability in the historical data. We control across-trial conditional error rates given a final NI trial design over a design specific robust range for reference effects. Following a conditionality principle, we provide a theoretical justification of the framework and the conditions for controlling across-trial unconditional type 1 error rates. We raise the issue of inherent bias in historical data with an illustrative example.

The Discover artificial disc replacement versus fusion in cervical radiculopathy--a randomized controlled outcome trial with 2-year follow-up

BACKGROUND CONTEXT

Several previous studies comparing artificial disc replacement (ADR) and fusion have been conducted with cautiously positive results in favor of ADR. This study is not, in contrast to most previous studies, an investigational device exemption study required by the Food and Drug Administration for approval to market the product in the United States. This study was partially funded with unrestricted institutional research grants by the company marketing the artificial disc used in this study.

PURPOSE

To compare outcomes between the concepts of an artificial disc to treatment with anterior cervical decompression and fusion (ACDF) and to register complications associated to the two treatments during a follow-up time of 2 years.

STUDY DESIGN/SETTING

This is a randomized controlled multicenter trial, including three spine centers in Sweden.

PATIENT SAMPLE

The study included patients seeking care for cervical radiculopathy who fulfilled inclusion criteria. In total, 153 patients were included.

OUTCOME MEASURES

Self-assessment with Neck Disability Index (NDI) as a primary outcome variable and EQ-5D and visual analog scale as secondary outcome variables.

METHODS

Patients were randomly allocated to either treatment with the Depuy Discover artificial disc or fusion with iliac crest bone graft and plating. Randomization was blinded to both patient and caregivers until time for implantation. Adverse events, complications, and revision surgery were registered as well as loss of follow-up.

RESULTS

Data were available in 137 (91%) of the included and initially treated patients. Both groups improved significantly after surgery. NDI changed from 63.1 to 39.8 in an intention-to-treat analysis. No statistically significant difference between the ADR and the ACDF groups could be demonstrated with NDI values of 39.1 and 40.1, respectively. Nor in secondary outcome measures (EQ-5D and visual analog scale) could any statistically significant differences be demonstrated between the groups. Nine patients in the ADR group and three in the fusion group underwent secondary surgery because of various reasons. Two patients in each group underwent secondary surgery because of adjacent segment pathology. Complication rates were not statistically significant between groups.

CONCLUSIONS

Artificial disc replacement did not result in better outcome compared to fusion measured with NDI 2 years after surgery.

Noninferiority studies with multiple reference treatments

The increasing popularity of noninferiority trials reflects the ongoing efforts to replace existing treatments (reference treatments) with new treatments (experimental treatments) that retain a substantial fraction of the effect of the reference treatments. The adoption of any new treatment has to be vindicated by a demonstration of benefits that outweigh a possible clinically insignificant reduction in the reference treatment efficacy. Statistical methods have been developed to analyze data collected from noninferiority trials. However, these methods focus on cases with only one reference treatment. In this paper, we provide the statistical inferential procedures for situations with multiple reference treatments. The computation of the corresponding critical values for simultaneous testings of noninferiority of several new treatments to multiple reference treatments in the presence of a placebo is provided. Furthermore, for a prespecified level of test power, a technique to determine the optimal sample size before the onset of a noninferiority trial is derived. A clinical example is given to illustrate our proposed procedure.

A simulation study evaluating bio-creep risk in serial non-inferiority clinical trials for preservation of effect

In non-inferiority trials, acceptable efficacy of an experimental treatment is established by ruling out some defined level of reduced effect relative to an effective active control standard. Serial use of non-inferiority trials may lead to newly approved therapies that provide meaningfully reduced levels of benefit; this phenomenon is called bio-creep. Simulations were designed to facilitate understanding of bio-creep risk when approval of an experimental treatment with efficacy less than some proportion of the effect of the active control treatment would constitute harm, such as when new antibiotics that are meaningfully less effective than the most effective current antibiotic would be used for treatment of Community-Acquired Bacterial Pneumonia. In this setting, risk of approval of insufficiently effective therapies may be great, even when the standard treatment effect satisfies constancy across trials. Modifiable factors contributing to this manifestation of bio-creep included the active control selection method, the non-inferiority margin, and bias in the active control effect estimate. Therefore, when non-inferiority testing is performed, the best available treatment should be used as the standard, and margins should be based on the estimated effect of this control, accounting for the variability and for likely sources of bias in this estimate, and addressing the importance of preservation of some portion of the standard's effect.

Treatment crossovers in time-to-event non-inferiority randomised trials of radiotherapy in patients with breast cancer

BACKGROUND

In non-inferiority trials of radiotherapy in patients with early stage breast cancer, it is inevitable that some patients will cross over from the experimental arm to the standard arm prior to initiation of any treatment due to complexities in treatment planning or subject preference. Although the intention-to-treat (ITT) analysis is the preferred approach for superiority trials, its role in non-inferiority trials is still under debate. This has led to the use of alternative approaches such as the per-protocol (PP) analysis or the as-treated (AT) analysis, despite the inherent biases of such approaches.

METHODS

Using simulations, we investigate the effect of 2%, 5% and 10% random and non-random crossovers prior to radiotherapy initiation on the ITT, PP, AT and the combination of ITT and PP analyses with respect to type I error in trials with time-to-event outcomes. We also evaluate bias and SE of the estimates from the ITT, PP and AT approaches.

RESULTS

The AT approach had the best performance in terms of type I error, but was anticonservative as non-random crossover increased. The ITT and PP approaches were anticonservative under all percentages of random and non-random crossover. Similarly, lowest bias was seen with the AT approach; however, bias increased as the percentage of non-random crossover increased. The ITT and PP had poor performance in terms of bias as crossovers increased.

CONCLUSIONS

If minimal crossovers were to occur, we have shown that the AT approach has the lowest type I error rates and smallest opportunity for bias. Results of trials with a high number of crossovers should be interpreted with caution, especially when crossover is non-random. Attempts to prevent crossovers should be maximised.

Choice of non-inferiority (NI) margins does not protect against degradation of treatment effects on an average--an observational study of registered and published NI trials

OBJECTIVE

NI margins have to be chosen appropriately to control the risk of degradation of treatment effects in non-inferiority (NI) trials. We aimed to study whether the current choice of NI margins protects sufficiently against a degradation of treatment effect on an average.

STUDY DESIGN AND SETTING

NI trials reflecting current practice were assembled and for each trial, the NI margin was translated into a likelihood of degradation. The likelihood of degradation was calculated as the conditional probability of a treatment being harmful given that it is declared non-inferior in the trial, using simulation. Its distribution among the NI trials was then studied to assess the potential risk of degradation.

RESULTS

The median (lower/upper quartile) NI margin among 112 binary outcome NI trials corresponded to an odds ratio of 0.57(0.45, 0.66), while among 38 NI trials with continuous outcome, to a Cohen's d of -0.42(-0.54, -0.31) and a hazard ratio of 0.82(0.73, 0.86) among 24 survival outcome NI trials. Overall, the median likelihood of degradation was 56% (45%, 62%).

CONCLUSION

Only two fifths of the current NI trials had a likelihood of degradation lower than 50%, suggesting that, in majority of the NI trials, there is no sufficient protection against degradation on an average. We suggest a third hurdle for the choice of NI margins, thus contributing a sufficient degree of protection.

Noninferiority Studies with Multiple New Treatments and Heterogeneous Variances

The objective of a noninferiority (NI) trial is to affirm the efficacy of a new treatment compared with an active control by verifying that the new treatment maintains a considerable portion of the treatment effect of the control. Compensation by benefits other than efficacy is usually the justification for using a new treatment, as long as the loss of efficacy is within an acceptable margin (NI margin) from the standard treatment. A popular approach is to express this margin in terms of the efficacy difference between the new treatment and the active control. Based on this approach and the realization that NI trials often comprise several new treatments, statistical procedures that simultaneously conduct NI tests of several new treatments have been developed. However, these procedures rely on the assumption that the variances of the treatments are homogeneous. In this article, we discuss the undesirable effect of using these procedures on the familywise Type I error rate when the treatment responses have heterogeneous variances. To alleviate this problem, we reveal potential procedures that are more appropriate. Further, a power study is conducted to compare the different procedures to provide guidance on the selection of adequate testing procedures in NI trials. Clinical examples are given for illustrative purposes.

New trial designs and potential therapies for pulmonary artery hypertension

A greater understanding of the epidemiology, pathogenesis, and pathophysiology of pulmonary artery hypertension (PAH) has led to significant advances, but the disease remains fatal. Treatment options are neither universally available nor always effective, underscoring the need for development of novel therapies and therapeutic strategies. Clinical trials to date have provided evidence of efficacy, but were limited in evaluating the scope and duration of treatment effects. Numerous potential targets in varied stages of drug development exist, in addition to novel uses of familiar therapies. The pursuit of gene and cell-based therapy continues, and device use to help acute deterioration and chronic management is emerging. This rapid surge of drug development has led to multicenter pivotal clinical trials and has resulted in novel ethical and global clinical trial concerns. This paper will provide an overview of the opportunities and challenges that await the development of novel treatments for PAH.