Strategies to improve retention in randomised trials

Abstract

BackgroundLoss to follow-up from randomised trials can introduce bias and reduce study power, affecting the generalisability, validity and reliability of results. Many strategies are used to reduce loss to follow-up and improve retention but few have been formally evaluated.ObjectivesTo quantify the effect of strategies to improve retention on the proportion of participants retained in randomised trials and to investigate if the effect varied by trial strategy and trial setting.Search methodsWe searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, PreMEDLINE, EMBASE, PsycINFO, DARE, CINAHL, Campbell Collaboration's Social, Psychological, Educational and Criminological Trials Register, and ERIC. We handsearched conference proceedings and publication reference lists for eligible retention trials. We also surveyed all UK Clinical Trials Units to identify further studies.Selection criteriaWe included eligible retention trials of randomised or quasi-randomised evaluations of strategies to increase retention that were embedded in 'host' randomised trials from all disease areas and healthcare settings. We excluded studies aiming to increase treatment compliance.Data collection and analysisWe contacted authors to supplement or confirm data that we had extracted. For retention trials, we recorded data on the method of randomisation, type of strategy evaluated, comparator, primary outcome, planned sample size, numbers randomised and numbers retained. We used risk ratios (RR) to evaluate the effectiveness of the addition of strategies to improve retention. We assessed heterogeneity between trials using the Chi2 and I2 statistics. For main trials that hosted retention trials, we extracted data on disease area, intervention, population, healthcare setting, sequence generation and allocation concealment.Main resultsWe identified 38 eligible retention trials. Included trials evaluated six broad types of strategies to improve retention. These were incentives, communication strategies, new questionnaire format, participant case management, behavioural and methodological interventions. For 34 of the included trials, retention was response to postal and electronic questionnaires with or without medical test kits. For four trials, retention was the number of participants remaining in the trial. Included trials were conducted across a spectrum of disease areas, countries, healthcare and community settings. Strategies that improved trial retention were addition of monetary incentives compared with no incentive for return of trial-related postal questionnaires (RR 1.18; 95% CI 1.09 to 1.28, P value < 0.0001), addition of an offer of monetary incentive compared with no offer for return of electronic questionnaires (RR 1.25; 95% CI 1.14 to 1.38, P value < 0.00001) and an offer of a GBP20 voucher compared with GBP10 for return of postal questionnaires and biomedical test kits (RR 1.12; 95% CI 1.04 to 1.22, P value < 0.005). The evidence that shorter questionnaires are better than longer questionnaires was unclear...

Enclosing a pen reduced time to response to questionnaire mailings

“…We searched the recent Cochrane systematic review of interventions to reduce trial attrition for embedded trials of enclosing a pen with a questionnaire mailing and found a single study by Sharp and colleagues (described previously [10]). We combined the results of this study with ours in a fixed effects meta-analysis.…”

“…There have been a number of systematic reviews appraising the literature surrounding non-monetary incentives to increase response rates [3,7,10]. Together, these have identified five trials evaluating the effect of adding a pen or pencil to postal mail outs on response rate [11][12][13][14].…”

“…Two of these aimed to increase response rates to stand-alone surveys, one to clinicians [12] and one to smokers [11], one aimed to increase response to a study recruitment invitation [14], and two aimed to increase response to a study follow-up survey [13,14]. Only one of these trials took the same methodological approach as the present work, embedding a trial of including a pen to increase response rate within an ongoing host trial [10]. The study was a 2x2x2 factorial trial embedded within the TOMBOLA study (Trial Of Management of Borderline and Other Low grade Abnormal smears) of cervical cytology surveillance, evaluating the effect on response rates of: i) enclosing a TOMBOLA-branded pen with the questionnaire; ii) sending the questionnaires by first class post (as opposed to second class); and iii) enclosing a preaddressed return envelope on which there was a second class postage stamp (rather than a freepost business-reply envelope) [13].…”

Text messaging research participants as a follow-up strategy to decrease emergency department study attrition

“…This study did not address other methods that could be used to mitigate loss to follow-up, such as monetary incentives, which have been previously shown to improve response rates. 7 However, the use of monetary incentives carries both practical and ethical considerations, particularly in the context of a clinical trial. Given that email has also been effective at decreasing study attrition for postal questionnaires, email may be another effective, low-cost option to use going forward.…”

“…[4][5][6] Despite the widespread application of text messaging to facilitate health care delivery, there is a paucity in the literature supporting the use of text messaging to facilitate clinical research, specifically to assist in research participant follow-up. 7 Incomplete or missing outcome data from patients lost to follow-up or patients who withdraw from study participation present a major threat to the internal and external validity of a clinical trial. The study results may be biased if patients are unable to follow up because of factors related to the outcome of interest.…”