Sensitivity Analysis for Not-at-Random Missing Data in Trial-Based Cost-Effectiveness Analysis : A Tutorial

Cost-effectiveness analyses (CEA) of randomised controlled trials are a key source of information for health care decision makers. Missing data are, however, a common issue that can seriously undermine their validity. A major concern is that the chance of data being missing may be directly linked to the unobserved value itself [missing not at random (MNAR)]. For example, patients with poorer health may be less likely to complete quality-of-life questionnaires. However, the extent to which this occurs cannot be ascertained from the data at hand. Guidelines recommend conducting sensitivity analyses to assess the robustness of conclusions to plausible MNAR assumptions, but this is rarely done in practice, possibly because of a lack of practical guidance. This tutorial aims to address this by presenting an accessible framework and practical guidance for conducting sensitivity analysis for MNAR data in trial-based CEA. We review some of the methods for conducting sensitivity analysis, but focus on one particularly accessible approach, where the data are multiply-imputed and then modified to reflect plausible MNAR scenarios. We illustrate the implementation of this approach on a weight-loss trial, providing the software code. We then explore further issues around its use in practice

Evaluation of a weighting approach for performing sensitivity analysis after multiple imputation

Abstract Background Multiple imputation (MI) is a well-recognised statistical technique for handling missing data. As usually implemented in standard statistical software, MI assumes that data are ‘Missing at random’ (MAR); an assumption that in many settings is implausible. It is not possible to distinguish whether data are MAR or ‘Missing not at random’ (MNAR) using the observed data, so it is desirable to discover the impact of departures from the MAR assumption on the MI results by conducting sensitivity analyses. A weighting approach based on a selection model has been proposed for performing MNAR analyses to assess the robustness of results obtained under standard MI to departures from MAR. Methods In this article, we use simulation to evaluate the weighting approach as a method for exploring possible departures from MAR, with missingness in a single variable, where the parameters of interest are the marginal mean (and probability) of a partially observed outcome variable and a measure of association between the outcome and a fully observed exposure. The simulation studies compare the weighting-based MNAR estimates for various numbers of imputations in small and large samples, for moderate to large magnitudes of departure from MAR, where the degree of departure from MAR was assumed known. Further, we evaluated a proposed graphical method, which uses the dataset with missing data, for obtaining a plausible range of values for the parameter that quantifies the magnitude of departure from MAR. Results Our simulation studies confirm that the weighting approach outperformed the MAR approach, but it still suffered from bias. In particular, our findings demonstrate that the weighting approach provides biased parameter estimates, even when a large number of imputations is performed. In the examples presented, the graphical approach for selecting a range of values for the possible departures from MAR did not capture the true parameter value of departure used in generating the data. Conclusions Overall, the weighting approach is not recommended for sensitivity analyses following MI, and further research is required to develop more appropriate methods to perform such sensitivity analyses

Clinical and functional differences between early-onset and late-onset adult asthma: a population-based Tasmanian Longitudinal Health Study

Differences between early-onset and late-onset adult asthma have not been comprehensively described using prospective data.To characterise the differences between early-onset and late-onset asthma in a longitudinal cohort study.The Tasmanian Longitudinal Health Study (TAHS) is a population-based cohort. Respiratory histories and spirometry were first performed in 1968 when participants were aged 7 (n=8583). The cohort was traced and resurveyed from 2002 to 2005 (n=5729 responses) and a sample, enriched for asthma and bronchitis participated in a clinical study when aged 44 (n=1389).Of the entire TAHS cohort, 7.7% (95% CI 6.6% to 9.0%) had early-onset and 7.8% (95% CI 6.4% to 9.4%) late-onset asthma. Atopy and family history were more common in early-onset asthma while female gender, current smoking and low socioeconomic status were more common in late-onset asthma. The impact on lung function of early-onset asthma was significantly greater than for late-onset asthma (mean difference prebronchodilator (BD) FEV/FVC -2.8% predicted (-5.3 to -0.3); post-BD FEVFVC -2.6% predicted (-5.0 to -0.1)). However, asthma severity and asthma score did not significantly differ between groups. An interaction between asthma and smoking was identified and found to be associated with greater fixed airflow obstruction in adults with late-onset asthma. This interaction was not evident in adults with early-onset disease.Early-onset and late-onset adult asthma are equally prevalent in the middle-aged population. Major phenotypic differences occur with asthma age-of-onset; while both share similar clinical manifestations, the impact on adult lung function of early-onset asthma is greater than for late-onset asthma

Supported progressive resistance exercise training to counter the adverse side effects of robot-assisted radical prostatectomy: a randomised controlled trial.

To investigate the effects of a supported home-based progressive resistance exercise training (RET) programme on indices of cardiovascular health, muscular strength and health-related quality of life (HR-QoL) in prostate cancer (PCa) patients after treatment with robot-assisted radical prostatectomy (RARP). This study was a single-site, two-arm randomised controlled trial, with 40 participants randomised to either the intervention or control group over a 10-month period. In addition to receiving usual care, the intervention group completed three weekly RET sessions using resistance bands for 6 months. Participants performed 3 sets of 12–15 repetitions for each exercise, targeting each major muscle group. The control group received usual care only. Brachial artery flow-mediated dilatation (FMD) was the primary outcome and assessed at baseline, 3 and 6 months. Secondary outcomes included body weight, body fat, aerobic fitness, strength and blood-borne biomarkers associated with cardiometabolic risk. There was no significant difference between the groups in FMD at 3 or 6 months. However, there were improvements in aerobic exercise capacity (P < 0.01) and upper- (P < 0.01) and lower-limb (P = 0.01) strength in favour of the RET group at 6 months, accompanied by greater weight loss (P = 0.04) and a reduction in body fat (P = 0.02). Improvements in HRQoL were evident in the RET group at 3 and 6 months via the PCa-specific component of the FACT-P questionnaire (both P < 0.01). Five adverse events and one serious adverse event were reported throughout the trial duration. This study demonstrates that home-based RET is an effective and safe mode of exercise that elicits beneficial effects on aerobic exercise capacity, muscular strength and HR-QoL in men who have undergone RARP.The Urology Foundatio