Although the efficacy of smartphone-delivered interventions for mental health problems is emerging, randomized controlled trials (RCTs) of smartphone interventions are characterized by high rates of attrition and low adherence. High attrition and low adherence may threaten the validity of RCT findings, so a better understanding of these phenomena is needed. We examined attrition and adherence in 70 RCTs of smartphone interventions. Four online databases were searched for RCTs of mental health interventions delivered via smartphones. The mean meta-analytic study attrition rate was 24.1% (95% CI [19.3, 29.6]) at short-term follow up and 35.5% (95% CI [26.7, 45.3]) at longer-term follow up. These rates varied according to target mental health condition. Attrition rates were significantly lower in trials that delivered an acceptance-based intervention, offered participants monetary compensation, and reminded participants to engage in the intervention, and were significantly higher in trials that used an online enrollment method (relative to telephone or in-person enrollment). No participant-level baseline characteristic reliably predicted attrition. Evidence of attrition bias came from many RCTs not conducting intention-to-treat analyses. However, the mean difference in the between-groups effect size on primary outcomes in trials that reported both per protocol an intention-to-treat analyses was only Δd = 0.18. Adherence rates were also suboptimal based on our qualitative synthesis; several participants failed to download the intervention, and intervention usage consistently declined over the course of the trial. Study attrition and low adherence are common, problematic, and may undermine the validity of findings in RCTs of smartphone-delivered interventions for mental health problems. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Participant retention strategies that minimise attrition in longitudinal cohort studies have evolved considerably in recent years. This study aimed to assess, via systematic review and meta-analysis, the effectiveness of both traditional strategies and contemporary innovations for retention adopted by longitudinal cohort studies in the past decade. Health research databases were searched for retention strategies used within longitudinal cohort studies published in the 10-years prior, with 143 eligible longitudinal cohort studies identified (141 articles; sample size range: 30 to 61,895). Details on retention strategies and rates, research designs, and participant demographics were extracted. Meta-analyses of retained proportions were performed to examine the association between cohort retention rate and individual and thematically grouped retention strategies. Results identified 95 retention strategies, broadly classed as either: barrier-reduction, community-building, follow-up/reminder, or tracing strategies. Forty-four of these strategies had not been identified in previous reviews. Meta-regressions indicated that studies using barrier-reduction strategies retained 10% more of their sample (95%CI [0.13 to 1.08]; p = .01); however, studies using follow-up/reminder strategies lost an additional 10% of their sample (95%CI [− 1.19 to − 0.21]; p = .02). The overall number of strategies employed was not associated with retention. Employing a larger number of retention strategies may not be associated with improved retention in longitudinal cohort studies, contrary to earlier narrative reviews. Results suggest that strategies that aim to reduce participant burden (e.g., flexibility in data collection methods) might be most effective in maximising cohort retention.

Objective: The present meta‐analysis summarizes existing evidence on the relationship between the internalization of body shape ideals (IBSI) and body dissatisfaction.Method: Pooled effect sizes (r) were computed using a random‐effects model. The robustness of the results was examined using influence analyses. Potential predictors of effect heterogeneity were examined using subgroup analysis and univariable/multivariable meta‐regressions. Publication bias was examined using the three‐parameter selection model (3PSM).Results: A total of 141 effect‐sizes from 78 studies (N = 39,491) were retrieved. Results revealed medium (r = .25; muscular/athletic‐ideal internalization) to very large (r = .43, general attractiveness‐ideal internalization; and r = .45, thin‐ideal internalization) relationships, all these being largely similar in male and female individuals.Discussion: IBSI and body dissatisfaction were strongly linked: (a) in younger individuals (general attractiveness‐ideal internalization); (b) when IBSI was operationalized in terms of endorsement rather than mere awareness of appearance ideals; (c) in studies of lower methodological quality (muscular/athletic‐ideal internalization); and (d) when IBSI was assessed using instruments involving social comparisons. Given the largely cross‐sectional nature of data included in this meta‐analysis, further testing in prospective and experimental studies is needed to confirm hypotheses about causality of observed associations. Such findings would have impact for prevention and intervention studies.