Sampling bias in an internet treatment trial for depression

L Donkin,I B Hickie,H Christensen,N L Cockayne,N Glozier,S L Naismith,B Neal

doi:10.1038/tp.2012.100

Abstract

Internet psychological interventions are efficacious and may reduce traditional access barriers. No studies have evaluated whether any sampling bias exists in these trials that may limit the translation of the results of these trials into real-world application. We identified 7999 potentially eligible trial participants from a community-based health cohort study and invited them to participate in a randomized controlled trial of an online cognitive behavioural therapy programme for people with depression. We compared those who consented to being assessed for trial inclusion with nonconsenters on demographic, clinical and behavioural indicators captured in the health study. Any potentially biasing factors were then assessed for their association with depression outcome among trial participants to evaluate the existence of sampling bias. Of the 35 health survey variables explored, only 4 were independently associated with higher likelihood of consenting—female sex (odds ratio (OR) 1.11, 95% confidence interval (CI) 1.05–1.19), speaking English at home (OR 1.48, 95% CI 1.15–1.90) higher education (OR 1.67, 95% CI 1.46–1.92) and a prior diagnosis of depression (OR 1.37, 95% CI 1.22–1.55). The multivariate model accounted for limited variance (C-statistic 0.6) in explaining participation. These four factors were not significantly associated with either the primary trial outcome measure or any differential impact by intervention arm. This demonstrates that, among eligible trial participants, few factors were associated with the consent to participate. There was no indication that such self-selection biased the trial results or would limit the generalizability and translation into a public or clinical setting.

Highlights

An increasing number of studies have demonstrated that internet-delivered, or online, health interventions for depression and anxiety are both efficacious,[1,2,3,4,5] and can be delivered to a population on a large scale.[1,6,7,8,9,10] These interventions have the potential to overcome traditional access barriers as they can be available anytime to individuals at low cost, and without waiting lists that are common for traditional face-toface interventions
We identified 7999 potentially eligible trial participants from a community-based health cohort study and invited them to participate in a randomized controlled trial of an online cognitive behavioural therapy programme for people with depression
The aim of this study was to (1) identify the factors associated with self-selection of eligible trial participants recruited from a large community health cohort study into a randomized controlled trial of an online depression treatment trial and (2) evaluate whether these factors were associated with outcome and potentially a source of sampling bias

Summary

Introduction

An increasing number of studies have demonstrated that internet-delivered, or online, health interventions for depression and anxiety are both efficacious,[1,2,3,4,5] and can be delivered to a population on a large scale.[1,6,7,8,9,10] These interventions have the potential to overcome traditional access barriers as they can be available anytime to individuals at low cost, and without waiting lists that are common for traditional face-toface interventions. Guidelines from the United Kingdom’s National Health Service (NHS),[12,13] the Scottish Intercollegiate Guidelines Network (SIGN)[14] and the Department of Veteran’s Affairs in the United States[15] have endorsed online interventions as part of stepped care management of depression. It seems likely that other countries will follow in the near future as further studies become available

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