Revealing the role of the gut microbiota in enhancing targeted therapy efficacy for lung adenocarcinoma

Lung adenocarcinoma (LUAD) is the leading cause of cancer-related death globally. Although the gut microbiota's role in the antitumor efficacy of many cancers has been revealed, its involvement in the response to gefitinib therapy for LUAD remains unclear. To fill this gap, we conducted a longitudinal study that profiled gut microbiota changes in PC-9 tumor-bearing mice under different treatments, including gefitinib monotherapy and combination therapies with probiotics, antibiotics, or Traditional Chinese Medicine (TCM). Our findings demonstrated that combining probiotics or TCM with gefitinib therapy outperformed gefitinib monotherapy, as evidenced by tumor volume, body weight, and tumor marker tests. By contrast, antibiotic intervention suppressed the antitumor efficacy of gefitinib. Notably, the temporal changes in gut microbiota were strongly correlated with the different treatments, prompting us to investigate whether there is a causal relationship between gut microbiota and the antitumor efficacy of gefitinib using Mediation Analysis (MA). Finally, our research revealed that thirteen mediators (Amplicon Sequence Variants, ASVs) regulate the antitumor effect of gefitinib, regardless of treatment. Our study provides robust evidence supporting the gut microbiota's significant and potentially causal role in mediating gefitinib treatment efficacy in mice. Our findings shed light on a novel strategy for antitumor drug development by targeting the gut microbiota.

Does trait mindfulness mediate the relationship between borderline personality symptoms and emotion dysregulation?

BACKGROUND

Emotion dysregulation is core to many biopsychosocial models of Borderline Personality Disorder (BPD) and is often targeted as part of their associated psychological therapies. Several distinct specialist psychotherapies are thought to be effective for people diagnosed with BPD but it is unclear whether they share common change mechanisms. Some evidence suggests that Mindfulness Based Interventions improve competency in emotion regulation as well as trait mindfulness, which are both plausibly associated with good treatment outcomes. It is unclear whether the association between the severity of BPD symptoms and emotion dysregulation is mediated by trait mindfulness. Would improvement in trait mindfulness mediate an association between lower severity of BPD symptoms and fewer problems of emotion dysregulation?

METHODS

One thousand and twelve participants completed online, single time-point, self-report questionnaires.

RESULTS

As predicted, the severity of BPD symptoms was significantly and positively associated with emotion dysregulation with a large effect size (r = .77). Trait mindfulness mediated this relationship as the 95% confidence interval for the indirect effect did not cross zero (size of direct effect = .48 and size of indirect effect = .29 [.25, .33].

CONCLUSIONS

The relationship between the severity of BPD symptoms and emotion dysregulation was confirmed in this dataset. As hypothesised, this relationship was mediated by trait mindfulness. Process measures of emotion dysregulation and mindfulness should be included in intervention studies for people diagnosed with BPD to understand if improvements in these factors are a universal occurrence with good response to treatment. Other process measures should also be explored to identify other factors involved in the relationship between BPD symptoms and emotion dysregulation.

[Pathway Analysis on the Effects of Nursing Informatics Competency, Nursing Care Left Undone, and Nurse Reported Quality of Care on Nursing Productivity among Clinical Nurses]

PURPOSE

Nursing informatics competency is used to manage and improve the delivery of safe, high-quality, and efficient healthcare services in accordance with best practices and professional and regulatory standards. This study examined the relationship between nursing informatics competency (NIC), nursing care left undone, and nurse reported quality of care (NQoC) and nursing productivity. A path model for their effects on nursing productivity among clinical nurses was also established.

METHODS

Data were collected using structured questionnaires answered by 192 nurses working in a tertiary hospital located in J city, Korea, and analyzed using SPSS/WIN 23.0 and AMOS 21.0 program.

RESULTS

The fit indices of the alternative path model satisfied recommended levels χ² = .11 (p = .741), normed χ² (χ²/df) = .11, SRMR = .01, RMSEA = .00, GFI = 1.00, NFI = 1.00, AIC = 18.11. Among the variables, NIC (β = .44, p < .001), NQoC (β = .35, p < .001) had a direct effect on nursing productivity. Due to the mediating effect of NQoC on the relationship between NIC and nursing productivity, the effect size was .14 (95% CI .08~.24). Meanwhile, nursing care left undone through NQoC in the relationship between NIC and nursing productivity, has a significant mediation effect (estimate .01, 95% CI .00~.03). The explanatory power of variables was 44.0%.

CONCLUSION

Education and training for enhancing NIC should be provided to improve nursing productivity, quality of care and to reduce missed nursing care. Furthermore, monitoring the quality of nursing care and using it as a productivity index is essential.

Social deprivation reduced registration for kidney transplantation through markers of nephrological care: a mediation analysis

OBJECTIVES

We assessed the direct and indirect effect of social deprivation mediated by modifiable markers of nephrological follow-up on registration on the renal transplantation waiting-list.

STUDY DESIGN AND SETTINGS

From the Renal Epidemiology and Information Network, we included French incident dialysis patients eligible for a registration evaluation between January 2017 and June 2018. Mediation analyses were conducted to assess effects of social deprivation estimated by quintile 5 (Q5) of the European Deprivation Index on registration defined as wait-listing at dialysis start or within the first 6 months.

RESULTS

Among the 11655 included patients, 2410 were registered. Q5 had a direct effect on registration (OR 0.82 [0.80-0.84]) and an indirect effect mediated by emergency start dialysis (OR 0.97 [0.97-0.98]), hemoglobin < 11 g/dL and/or lack of EPO (OR 0.96 [0.96-0.96]) and albumin < 30 g/L (OR 0.98 [0.98-0.99]).

CONCLUSION

Social deprivation was directly associated with a lower registration on the renal transplantation waiting-list but its effect was also mediated by markers of nephrological care, suggesting that improving the follow-up of the most deprived patients should help to reduce disparities in access to transplantation.

Mediation Analysis in Manual Therapy Research

Objective

The purpose of this study was to illustrate the applicability of mediation analysis in the manual therapy field by assessing whether pain intensity, duration of pain, or the change in systolic blood pressure mediated the heart rate variability (HRV) of patients with musculoskeletal pain who received manual therapy.

Methods

A secondary data analysis from a 3-arm, parallel, randomized, placebo-controlled, assessor-blinded, superiority trial was performed. Participants were randomized into spinal manipulation, myofascial manipulation, or placebo groups. Cardiovascular autonomic control was inferred from resting HRV variables (low-high frequency power ratio; LF/HF) and blood pressure responsiveness to a sympathoexcitatory stimulus (cold pressor test). Pain intensity and duration were assessed. Mediation models analyzed whether pain intensity, duration, or blood pressure independently affected the improvement of the cardiovascular autonomic control of patients with musculoskeletal pain after intervention.

Results

The first assumption of mediation was met for LF/HF with statistical evidence of a total effect of spinal manipulation, as compared with placebo on HRV outcomes (β = 0.77 [0.17-1.30]); second and third assumptions showed no statistical evidence of a relationship between the intervention and pain intensity (β = -5.30 [-39.48 to 28.87]), pain intensity, and LF/HF (β = 0.00 [-0.01 to 0.01]).

Conclusion

In this study of causal mediation analysis, the baseline pain intensity, duration of pain, and responsiveness of the systolic blood pressure to a sympathoexcitatory stimulus did not mediate the effects of the spinal manipulation on the cardiovascular autonomic control of patients with musculoskeletal pain. Accordingly, the immediate effect of spinal manipulation on the cardiac vagal modulation of patients with musculoskeletal pain may more likely be related to the intervention rather than the mediators investigated.

Mediation Analysis and Mixed-Effects Models for the Identification of Stage-specific Imaging Genetics Patterns in Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common and severe forms of Senile Dementia. Genome-wide association studies (GWAS) have identified dozens of AD susceptible loci. To better understand potential mechanism-of-action for AD, quantitative brain imaging features have been studied as mediators linking genetic variants to AD outcomes. In this study, Mediation analysis, Chow test and Mixed-effects Models are used to investigate the biological pathways by which genetic variants affect both brain structures/functions and disease diagnosis. We analyzed the imaging and genetics data collected from the Alzheimer's Disease Neuroimaging Initiative (ADNI) project, including a Polygenic Hazard Score (PHS) and 13 imaging quantitative traits (QTs) extracted from the AV45 PET scans quantifying the amyloid deposition in different brain regions of subjects from four separate diagnostic groups. Mediation analysis assessed the mediating effects of image QTs between PHS and diagnosis, whereas Chow test and Linear Mixed-Effects models were used to characterize intra-group differences in the associations between genetic scores and imaging QTs for different disease stages. Results show that promising stage-specific imaging QTs that mediate the genetic effect of the studied PHS on disease status have been identified, providing novel insights into the predictive power of the PHS and the mediating power of amyloid imaging QTs with respect to multiple stages over the AD progression.

The mediating role of decision-making conflict in the association between patient's participation satisfaction and distress during medical decision-making among Chinese patients with pulmonary nodules

OBJECTIVE

When diagnosed as having pulmonary nodules, patients may be mired in the conflict of medical decision-making and suffered from distress. The purpose of this study was to investigate the mediating role of decision-making conflict in the relationship between participation satisfaction in medical decision-making (PSMD) and distress among Chinese patients with incidental pulmonary nodules.

METHODS

A total of 163 outpatients with incidental pulmonary nodules detected in a tertiary hospital were recruited and investigated by Impact of Event Scale (IES), Decision Conflict Scale (DCS), participation satisfaction in medical decision-making Scale (PSMDS), and demographic questionnaire.

RESULTS

The mean IES score was 37.35 ± 16.65, representing a moderate level. PSMD was negatively associated with distress, while decision-making conflict was positively associated with distress. The final regression model contained three factors: having a first-degree relative diagnosed with lung cancer, worrying about getting lung cancer someday, and decision-making conflict. These three factors explained 49.4 % of the variance of distress. The total effect of PSMD on distress and indirect effect of SPMD on distress caused-by decision-making conflict were significant (P < 0.05). However, the direct effect of PSMD on distress was not significant.

CONCLUSIONS

Participation of patients in medical decision-making can lower their distress by reducing patient's decision-making conflict.

PRACTICE IMPLICATIONS

Interventions targeting at the decision-making conflict will help alleviate the distress level of patients with pulmonary nodules.

DATA AVAILABILITY

The data that support the findings of this study are available on request from the corresponding author.

Mediterranean-Like Dietary Pattern Associations With Gut Microbiome Composition and Subclinical Gastrointestinal Inflammation

BACKGROUND & AIMS

Case-control studies have shown that patients with Crohn's disease (CD) have a microbial composition different from healthy individuals. Although the causes of CD are unknown, epidemiologic studies suggest that diet is an important contributor to CD risk, potentially via modulation of bacterial composition and gut inflammation. We hypothesized that long-term dietary clusters (DCs) are associated with gut microbiome compositions and gut inflammation. Our objectives were to identify dietary patterns and assess whether they are associated with alterations in specific gut microbial compositions and subclinical levels of gut inflammation in a cohort of healthy first-degree relatives (FDRs) of patients with CD.

METHODS

As part of the Genetic, Environmental, Microbial (GEM) Project, we recruited a cohort of 2289 healthy FDRs of patients with CD. Individuals provided stool samples and answered a validated food frequency questionnaire reflecting their habitual diet during the year before sample collection. Unsupervised analysis identified 3 dietary and 3 microbial composition clusters.

RESULTS

DC3, resembling the Mediterranean diet, was strongly associated with a defined microbial composition, with an increased abundance of fiber-degrading bacteria, such as Ruminococcus, as well as taxa such as Faecalibacterium. The DC3 diet was also significantly associated with lower levels of subclinical gut inflammation, defined by fecal calprotectin, compared with other dietary patterns. No significant associations were found between individual food items and fecal calprotectin, suggesting that long-term dietary patterns rather than individual food items contribute to subclinical gut inflammation. Additionally, mediation analysis demonstrated that DC3 had a direct effect on subclinical inflammation that was partially mediated by the microbiota.

CONCLUSIONS

Overall, these results indicated that Mediterranean-like dietary patterns are associated with microbiome and lower intestinal inflammation. This study will help guide future dietary strategies that affect microbial composition and host gut inflammation to prevent diseases.

[Influence of Learning Presence of Non-Face-to-Face Class Experience in Nursing Students on Academic Achievement: Mediating Effect of Learning Flow and Moderated Mediation of Digital Literacy]

PURPOSE

This study aimed to identify the mediating effect of learning flow and the moderated mediation effect of digital literacy on the effect of the learning presence of non-face-to-face class experience in nursing students on academic achievement.

METHODS

Participants were 272 nursing students from six universities in two different cities. A self-report questionnaire was used to measure learning presence, learning flow, digital literacy, and academic achievement. Analysis was performed using SPSS 26.0 and SPSS PROCESS Macro (4.0).

RESULTS

The mediating effect of learning flow on the effect of learning presence on academic achievement was 0.42, and the moderated mediation index of digital literacy was 0.17. Learning flow showed a mediating effect on the relationship between learning presence and academic achievement. Digital literacy had a moderated mediation effect on the relationship between learning presence and academic achievement that was mediated by learning flow.

CONCLUSION

The intensity of the mediating effect of nursing students' learning presence on academic achievement through learning flow increases as the level of digital literacy increases. These results suggest that educational programs considering the level of learning presence, learning flow, and digital literacy are required to promote the academic achievement of nursing college students.

Altruistic Social Activity, Depressive Symptoms, and Brain Regional Gray Matter Volume: Voxel-Based Morphometry Analysis from 8695 Old Adults

Altruistic social activity, such as giving support to others, has shown protective benefits on dementia risk and cognitive decline. However, the pathological mechanism is unclear. In the present study, we investigated the association between altruistic social activity and brain regional gray matter. Furthermore, to explore the psychological interplay in altruistic social activity, we tested mediating effect of depressive symptoms on brain regional gray matter. We performed a cross-sectional Voxel-Based Morphology (VBM) analysis including 8695 old adults (72.9±6.1 years) from Japan Prospective Studies Collaboration for Aging and Dementia (JPSC-AD) Cohort. We measured altruistic social activities by self-report questionnaire, depressive symptoms by Geriatric Depression Scale (GDS)-short version. We employed the whole-brain VBM method to detect relevant structural properties related to altruistic social activity. We then performed multiple regression models to detect the mediating effect of depressive symptoms on particular brain regional gray matter volume while adjusting possible physical and social lifestyle covariables. We found that altruistic social activity is associated with larger gray matter volume in posterior insula, middle cingulate gyrus, hippocampus, thalamus, superior temporal gyrus, anterior orbital gyrus, and middle occipital gyrus. Depressive symptoms mediated over 10% on altruistic social activity and hippocampus volume, over 20% on altruistic social activity and cingulate gyrus volume. Our results indicated that altruistic social activity might preserve brain regional gray matter where are sensitive to aging and cognitive decline. Meanwhile, this association may be explained by indirect effect on depressive symptoms, suggesting that altruistic social activity may mitigate the neuropathology of dementia.

Relationships between enriching early life experiences and cognitive function later in life are mediated by educational attainment

The study of how engagement in enriching cognitive, physical and social activities in childhood impacts cognitive function decades later will advance our understanding of how modifiable lifestyle activities promote cognition across the lifespan. 88 healthy older adults (aged 60-80 years) returned a retrospective questionnaire regarding their participation in seven lifestyle activities (musical instrument playing, language learning, sport participation, art/dance lessons, scouting, volunteering, family vacations) before age 13 years. After controlling for current age, educational attainment, socioeconomic status of the mother and current engagement in lifestyle activities, a greater number of activities were significantly associated with better vocabulary abilities, episodic memory and fluid intelligence. The relationships with vocabulary and fluid intelligence were mediated by educational attainment. We postulate that engagement in a higher number of enriching early life activities is a reflection of both one's sociocontextual environment and engagement with that environment. This engagement leads to attributes relevant for educational aspirations/attainment, ultimately contributing to factors that have a lifespan impact on cognitive function.

The Mediating Effect of Perceived Injustice and Pain Catastrophizing in the Relationship of Pain on Fatigue and Sleep in Breast Cancer Survivors: A Cross-Sectional Study

OBJECTIVE

Multidimensional aspects of pain have raised awareness about cognitive appraisals, such as perceived injustice (PI) and pain catastrophizing (PC). It has been demonstrated that they play an important role in patients' pain experience. However, the mediating effect of these appraisals has not been investigated in breast cancer survivors (BCS), nor have they been related to fatigue and sleep.

METHODS

Cross-sectional data from 128 BCS were analysed by structural path analysis with the aim to examine the mediating effect of PI and PC in the relationship of pain on fatigue and sleep.

RESULTS

The indirect mediating effects of PI on fatigue (CSI*PI = 0.21; P < 0.01 and VAS*PI = 1.19; P < 0.01) and sleep (CSI*PI = 0.31; P < 0.01 and VAS*PI = 1.74; P < 0.01) were found significant for both pain measures (Central Sensitization Inventory (CSI) and Visual Analogue Scale (VAS)). PC, on the other hand, only mediated the relationship between pain measured by VAS and fatigue (VAS*PC = 0.80; P = 0.03). Positive associations were found, indicating that higher pain levels are positively correlated with PI and PC, which go hand in hand with higher levels of fatigue and sleep problems.

CONCLUSION

PI is an important mediator in the relationship of pain on fatigue and sleep, while PC is a mediator on fatigue after cancer treatment. These findings highlight that both appraisals are understudied and open new perspectives regarding treatment strategies in BCS.

Lipids, Anthropometric Measures, Smoking and Physical Activity Mediate the Causal Pathway From Education to Breast Cancer in Women: A Mendelian Randomization Study

Purpose

We aimed to investigate whether obtaining a higher level of education was causally associated with lower breast cancer risk and to identify the causal mechanism linking them.

Methods

The main data analysis used publicly available summary-level data from 2 large genome-wide association study consortia. Mendelian randomization (MR) analysis used 65 genetic variants derived from the Social Science Genetic Association Consortium as instrumental variables for years of schooling. The outcomes from the Breast Cancer Association Consortium (BCAC) were the overall breast cancer risk (122,977 cases/105,974 controls in women) and the two subtypes: estrogen receptor (ER)-positive breast cancer and ER-negative breast cancer. Fixed and random effects inverse variance weighted methods were used to estimate the causal effects, along with other additional MR methods for sensitivity analyses.

Results

Results showed that each additional standard deviation of 4.2 years of education was causally associated with a 27% lower risk of ER-negative breast cancer (odds ratio, 0.73; 95% confidence interval, 0.64–0.84; p-value < 0.001). This finding was consistent with the results of the sensitivity analyses. Physical activities can help improve the protective effect of education against breast cancer, with relatively large mediation proportions. Education increases the risk of ER-positive breast cancer due to alterations in high-density lipoprotein level, triglyceride level, height, waist-to-hip ratio, body mass index, and smoking status, with relative medium mediation proportions. Other mediators including low-density lipoprotein, hip circumference, number of cigarettes smoked per day, time spent performing light physical activity, and performing vigorous physical activity for > 10 minutes explain a small part of the causal effect of education on the risk of developing breast cancer, and their mediation proportion is approximately 1%.

Conclusion

A low level of education is a causal risk factor in the development of breast cancer as it is associated with poor lipid profile, obesity, smoking, and types of physical activity.

Does Resiliency Mediate the Association of Psychological Adaptability with Limitations and Pain Intensity after Upper Extremity Trauma?

BACKGROUND

Given the influence of psychosocial factors on musculoskeletal symptoms and limitations, this study assessed if the ability of resilience (an individual's ability to adapt under stress) mediates the association of psychological adaptability with magnitude of physical limitations and pain intensity during recovery from an upper extremity injury.

METHODS

A total of 107 patients were enrolled in this prospective, longitudinal, observational cohort study. Patients completed the Patient-Reported Outcomes Measurement Information System Physical Function (PROMIS PF), an 11-point ordinal measure of pain intensity, the Brief Resilience Scale (BRS), and the Psychological Adaptation Scale (PAS). We used structural equation modeling to assess the mediation effect by resiliency and psychological adaptability on patient-reported disability and pain at initial assessment and after three months.

RESULTS

PAS and BRS were not independently associated with PROMIS PF or pain intensity at enrollment or after three months, so it was not possible to assess if resiliency mediated the association of psychological adaptability with physical function or pain. There were no factors independently associated with resilience.

CONCLUSION

General measures of psychological adaptability and resiliency do not correlate with symptoms and limitations as well as specific measures of adaptiveness in response to nociception.

The Link between Serum 25-Hydroxyvitamin D, Inflammation and Glucose/ Insulin Homeostasis Is Mediated By Adiposity Factors in American Adults

Prior studies have suggested a significant association between 25-hydroxyvitamin D (25(OH)D) concentrations with markers of inflammation and glucose and insulin homeostasis. However, it is unclear whether these associations are confounded or mediated by adiposity. We used an established mediation analysis to investigate the role of adiposity in the relation between serum 25(OH)D with markers of inflammation and glucose and insulin metabolism. We used data from National Health and Nutrition Examination Survey (2005-2010), to evaluate the associations between serum 25(OH)D and markers of insulin resistance or inflammation, and whether these associations are mediated by adiposity factors including body mass index (BMI, marker of body adiposity), waist circumference (WC, marker of central adiposity), anthropometrically predicted visceral adipose tissue (apVAT), and Visceral Adiposity Index (VAI). Analysis of co-variance and conceptual causal mediation analysis were conducted taking into consideration the survey design and sample weights. A total of 16,621 individuals were included; 8607 (48.3%) participants were men and the mean age of the population was 47.1 years. Mean 25(OH)D serum concentration for the overall population was 57.9±0.1 nmol/L with minimal differences between men and women (57.5±0.2 nmol/L and 58.2±0.2 nmol/L, respectively). After adjustment for age, sex, season and race/ethnicity, mean levels of C-reactive protein (CRP), apolipoprotein B (apo-B), fasting blood glucose (FBG), insulin, homeostatic model assessment of IR (HOMA-IR) and β cell function (HOMA-β), haemoglobin A1c (HbA1c), and 2-h glucose were lower for the top quartile of serum 25(OH)D (all p<0.001). Body mass index (BMI) was found to have significant mediation effects (to varied extent) on the associations between serum 25(OH)D and CRP, apo-B, fasting glucose, insulin, HOMA-IR, HOMA-B and HbA1c (all p<0.05). Both waist circumference and apVAT were also found to partly mediate the associations between serum 25(OH)D with CRP, FBG, HbA1c, triglycerides and HDL-cholesterol (all P < 0.05). VAI was found to have mediation effects on CRP only (p<0.001). Using a mediation model, our findings suggest that the relationship between serum 25(OH)D, insulin resistance and inflammation, may be in part mediated by adiposity. These findings support the importance of optimizing 25(OH)D status in conditions with abnormal adiposity (i.e., obesity) and treatments for the prevention of cardio-metabolic diseases affecting adipose tissue metabolism (i.e., weight loss).

Using SAS Macros for Multiple Mediation Analysis in R

Mediation analysis refers to the process of making inferences on effects of third variables that intervene in the relationship between an exposure and response variable. The relationships among variables can be modelled by generalized linear models (GLM). However, GLM are not sufficient to describe relationships among variables when there are nonlinear relationships and potential interaction effects. A general mediation analysis method was developed using not only GLMs, but also multiple additive regression trees and smoothing splines by Yu and Li (2017). The method is implemented in the R package, mma. In this paper, we developed SAS macros so that functions in the mma package can be called and the mediation analysis performed in the SAS environment.

Daily Control Beliefs and Cognition: The Mediating Role of Physical Activity

OBJECTIVES

Recent work suggests that physical activity may underlie the positive relationship between control beliefs and cognition. Despite the well-known cognitive benefits, most adults do not engage in enough physical activity, perhaps due to low perceived control. The current study aimed to expand upon past work by investigating these constructs over the short-term by studying the intraindividual variability in daily control beliefs, physical activity, and cognition. We examined whether these constructs were related on a day-to-day basis and if daily physical activity mediated the relationship between control beliefs and cognition.

METHOD

Over 7 consecutive days, 145 participants (M = 50.54 years) completed daily diaries to measure domain-specific control beliefs, wore an ActiGraph to capture objective physical activity, and were administered 2 tasks each day via phone to measure cognition.

RESULTS

Using multilevel structural equation modeling, our results indicated that on days with higher control beliefs cognition was also higher and this relationship was mediated by one's level of physical activity.

DISCUSSION

These findings demonstrate the role of physical activity in linking control beliefs and cognition on a daily level using a within-person approach to investigate the dynamic processes in beliefs and cognition.

Mechanism evaluation of a lifestyle intervention for patients with musculoskeletal pain who are overweight or obese: protocol for a causal mediation analysis

INTRODUCTION

Low back pain (LBP) and knee osteoarthritis (OA) are highly prevalent and disabling conditions that cause societal and economic impact worldwide. Two randomised controlled trials (RCTs) will evaluate the effectiveness of a multicomponent lifestyle intervention for patients with LBP and knee OA who are overweight or obese. The key targets of this intervention are to improve physical activity, modify diet and correct pain beliefs. These factors may explain how a lifestyle intervention exerts its effects on key patient-relevant outcomes: pain, disability and quality of life. The aim of this protocol is to describe a planned analysis of a mechanism evaluation for a lifestyle intervention for overweight or obese patients with LBP and knee OA.

METHODS AND ANALYSIS

Causal mediation analyses of 2 two-armed RCTs. Both trials are part of a cohort-multiple RCT, embedded in routine health service delivery. In each respective trial, 160 patients with LBP and 120 patients with knee OA waiting for orthopaedic consultation will be randomised to a lifestyle intervention, or to remain part of the original cohort. The intervention consists of education and advice about the benefits of weight loss and physical activity, and the Australian New South Wales Get Healthy Service. All outcome measures including patient characteristics, primary and alternative mediators, outcomes, and potential confounders will be measured at baseline (T0). The primary mediator, weight, will be measured at 6 months post randomisation; alternative mediators including diet, physical activity and pain beliefs will be measured at 6 weeks post randomisation. All outcomes (pain, disability and quality of life) will be measured at 6 months post randomisation. Data will be analysed using causal mediation analysis with sensitivity analyses for sequential ignorability. All mediation models were specified a priori before completing data collection and without prior knowledge about the effectiveness of the intervention.

ETHICS AND DISSEMINATION

The study is approved by the Hunter New England Health Human Research Ethics Committee (13/12/11/5.18) and the University of Newcastle Human Research Ethics Committee (H-2015-0043). The results will be disseminated in peer-reviewed journals and at scientific conferences.

TRIAL REGISTRATION NUMBER

ACTRN12615000490572 and ACTRN12615000478516; Pre-results.

Econometric Mediation Analyses: Identifying the Sources of Treatment Effects from Experimentally Estimated Production Technologies with Unmeasured and Mismeasured Inputs

This paper presents an econometric mediation analysis. It considers identification of production functions and the sources of output effects (treatment effects) from experimental interventions when some inputs are mismeasured and others are entirely omitted. JEL Code: D24, C21, C43, C38.

JOINT ANALYSIS OF SNP AND GENE EXPRESSION DATA IN GENETIC ASSOCIATION STUDIES OF COMPLEX DISEASES

Genetic association studies have been a popular approach for assessing the association between common Single Nucleotide Polymorphisms (SNPs) and complex diseases. However, other genomic data involved in the mechanism from SNPs to disease, e.g., gene expressions, are usually neglected in these association studies. In this paper, we propose to exploit gene expression information to more powerfully test the association between SNPs and diseases by jointly modeling the relations among SNPs, gene expressions and diseases. We propose a variance component test for the total effect of SNPs and a gene expression on disease risk. We cast the test within the causal mediation analysis framework with the gene expression as a potential mediator. For eQTL SNPs, the use of gene expression information can enhance power to test for the total effect of a SNP-set, which are the combined direct and indirect effects of the SNPs mediated through the gene expression, on disease risk. We show that the test statistic under the null hypothesis follows a mixture of χ² distributions, which can be evaluated analytically or empirically using the resampling-based perturbation method. We construct tests for each of three disease models that is determined by SNPs only, SNPs and gene expression, or includes also their interactions. As the true disease model is unknown in practice, we further propose an omnibus test to accommodate different underlying disease models. We evaluate the finite sample performance of the proposed methods using simulation studies, and show that our proposed test performs well and the omnibus test can almost reach the optimal power where the disease model is known and correctly specified. We apply our method to re-analyze the overall effect of the SNP-set and expression of the ORMDL3 gene on the risk of asthma.

Tests of Mediation: Paradoxical Decline in Statistical Power as a Function of Mediator Collinearity

Increasing the correlation between the independent variable and the mediator (a coefficient) increases the effect size (ab) for mediation analysis; however, increasing a by definition increases collinearity in mediation models. As a result, the standard error of product tests increase. The variance inflation due to increases in a at some point outweighs the increase of the effect size (ab) and results in a loss of statistical power. This phenomenon also occurs with nonparametric bootstrapping approaches because the variance of the bootstrap distribution of ab approximates the variance expected from normal theory. Both variances increase dramatically when a exceeds the b coefficient, thus explaining the power decline with increases in a. Implications for statistical analysis and applied researchers are discussed.