Test non-inferiority and sample size determination based on the odds ratio under a cluster randomized trial with noncompliance

What are the statistical implications of treatment non-compliance in cluster randomized trials: A simulation study

Subjects in randomized controlled trials do not always comply to the treatment condition they have been assigned to. This may cause the estimated effect of the intervention to be biased and also affect efficiency, coverage of confidence intervals, and statistical power. In cluster randomized trials non‐compliance may occur at the subject level but also at the cluster level. In the latter case, all subjects within the same cluster have the same compliance status. The purpose of this study is to investigate the statistical implications of non‐compliance in cluster randomized trials. A simulation study was conducted with varying degrees of non‐compliance at either the cluster level or subject level. The probability of non‐compliance depends on a covariate at the cluster or subject level. Various realistic values of the intraclass correlation coefficient and cluster size are used. The data are analyzed by intention to treat, as treated, per protocol and the instrumental variable approach. The results show non‐compliance may result in downward biased estimates of the intervention effect and an under‐ or overestimate of its standard deviation. The coverage of the confidence intervals may be too small, and in most cases, empirical power is too small. The results are more severe when the probability of non‐compliance increases and the covariate that affects compliance is unobserved. It is advocated to avoid non‐compliance. If this is not possible, compliance status and covariates that affect compliance should be measured and included in the statistical model.

Bayesian Design of Non-Inferiority Clinical Trials via the Bayes Factor

We developed a Bayes factor based approach for the design of non-inferiority clinical trials with a focus on controlling type I error and power. Historical data are incorporated in the Bayesian design via the power prior discussed in Ibrahim and Chen (2000). The properties of the proposed method are examined in detail. An efficient simulation-based computational algorithm is developed to calculate the Bayes factor, type I error and power. The proposed methodology is applied to the design of a non-inferiority medical device clinical trial.

Methods for sample size determination in cluster randomized trials

BACKGROUND

The use of cluster randomized trials (CRTs) is increasing, along with the variety in their design and analysis. The simplest approach for their sample size calculation is to calculate the sample size assuming individual randomization and inflate this by a design effect to account for randomization by cluster. The assumptions of a simple design effect may not always be met; alternative or more complicated approaches are required.

METHODS

We summarise a wide range of sample size methods available for cluster randomized trials. For those familiar with sample size calculations for individually randomized trials but with less experience in the clustered case, this manuscript provides formulae for a wide range of scenarios with associated explanation and recommendations. For those with more experience, comprehensive summaries are provided that allow quick identification of methods for a given design, outcome and analysis method.

RESULTS

We present first those methods applicable to the simplest two-arm, parallel group, completely randomized design followed by methods that incorporate deviations from this design such as: variability in cluster sizes; attrition; non-compliance; or the inclusion of baseline covariates or repeated measures. The paper concludes with methods for alternative designs.

CONCLUSIONS

There is a large amount of methodology available for sample size calculations in CRTs. This paper gives the most comprehensive description of published methodology for sample size calculation and provides an important resource for those designing these trials.

A review of prospective Clinical Trials for neurogenic bladder: The place of surgery, experimental techniques and devices

Introduction

The neurogenic urinary bladder has been known for at least 30 years now and the concepts behind it are continuously evolving, but there is actually not much work that has been done to accumulate solid clinical evidence in this field. We review the surgical and experimental techniques used in the management of this condition.

Material and methods

To achieve our goal, we performed Internet searches using the same search string: Urinary bladder, neurogenic. In each case, the search was limited to clinical trial, subjects were human and the language was English. After duplicate removal, we obtained a final number of 580 papers. Data was extracted from each paper into a database file and was analyzed separately for adult and pediatric populations.

Results

A total of 70 full text papers were reviewed and analyzed according to the previously mentioned algorithm. The first prospective, randomized surgical trials were published less than 20 years ago, starting with 1994, and the number of papers published each year since then has remained in the range of 1–3. The oldest prospective clinical trial for this indication dates back to 1975. The total number of patients included in surgical trials is 3453, out of which 59% are males. The papers include a total of 369 children (21.2%), essentially looking at all the techniques that are also used in adults.

Conclusions

There is still a lot of work to be done in order to obtain a significant level of evidence in the field of surgical procedures used in neurogenic bladder patients.

A review of prospective Clinical Trials for neurogenic bladder: Pharmaceuticals

Introduction

The neurogenic urinary bladder is defined as a dysfunctional bladder associated with a known neurological injury. We review the data from good quality clinical trials looking at drug therapy for the neurogenic bladder.

Materials and methods

In order to identify as many prospective trials as possible, we performed Internet searches, using the same search string: Urinary Bladder, neurogenic (MESH). In each case, the search was limited to clinical trial, prospective trial, subjects were human and the language was English. There was no year limit for our search. The next step was duplicate removal, which led to a final number of 580 papers. We defined clear inclusion criteria for the papers.

Results

A total of 82 full text papers were reviewed and analyzed according to the previously mentioned algorithm. The oldest two prospective clinical trials date back to 1976, with an obvious increase in number of trials each year, reaching more than five trials per year after 2001, which demonstrates increased interest toward the subject. The total number of patients included in the trials is 3904, 888 of which are children. The male: female ratio is close to 1, although there were 9 studies where no information regarding the sex of the patients was available.

Conclusions

Our analysis stresses the acute need for good quality trials looking at the drugs used for the management of the patients with neurogenic bladders, with adequate statistical power to support the data they present.