Exploratory randomized controlled trial evaluating the impact of a waiting list control design

John A Cunningham,Kypros Kypri,Jim Mccambridge

doi:10.1186/1471-2288-13-150

Abstract

BackgroundEmploying waiting list control designs in psychological and behavioral intervention research may artificially inflate intervention effect estimates. This exploratory randomized controlled trial tested this proposition in a study employing a brief intervention for problem drinkers, one domain of research in which waiting list control designs are used.MethodsAll participants (N = 185) were provided with brief personalized feedback intervention materials after being randomly allocated either to be told that they were in the intervention condition and that this was the intervention or to be told that they were in the waiting list control condition and that they would receive access to the intervention in four weeks with this information provided in the meantime.ResultsA total of 157 participants (85%) were followed-up after 4 weeks. Between-group differences were found in one of four outcomes (proportion within safe drinking guidelines). An interaction was identified between experimental manipulation and stage of change at study entry such that participant change was arrested among those more ready to change and told they were on the waiting list.ConclusionsTrials with waiting list control conditions may overestimate treatment effects, though the extent of any such bias appears likely to vary between study populations. Arguably they should only be used where this threat to valid inference has been carefully assessed.

Highlights

Employing waiting list control designs in psychological and behavioral intervention research may artificially inflate intervention effect estimates
While there are ethical advantages to a waiting list design because it allows for the provision of care to research participants who are seeking help, whilst permitting a non-intervention evaluation, it has been noted that such designs may overestimate intervention effects [1,2,3,4,5,6,7]
Previous studies have included a range of waiting list designs, some in which the participant is told that they will have to wait to receive treatment and others where a period of monitoring is described as a necessary baseline [14,15]

Summary

Introduction

Employing waiting list control designs in psychological and behavioral intervention research may artificially inflate intervention effect estimates. While there are ethical advantages to a waiting list design because it allows for the provision of care (if delayed) to research participants who are seeking help, whilst permitting a non-intervention evaluation, it has been noted that such designs may overestimate intervention effects [1,2,3,4,5,6,7]. This is because participants assigned to a waiting list control condition appear to improve less (or not at all) than would be expected for. Other factorial designs have been used to evaluate unintended impacts of the research process [17]

Methods

Results

Discussion

Conclusion