Impact of Length or Relevance of Questionnaires on Attrition in Online Trials:Randomized Controlled Trial

McCambridge, Jim, Kalaitzaki, Eleftheria, White, Ian R, Khadjesari, Zarnie, Murray, Elizabeth, Linke, Stuart, Thompson, Simon G, Godfrey, Christine and Wallace, Paul (2011) Impact of Length or Relevance of Questionnaires on Attrition in Online Trials:Randomized Controlled Trial. Journal of Medical Internet Research, 13 (4). ISSN 1439-4456

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BACKGROUND: There has been limited study of factors influencing response rates and attrition in online research. Online experiments were nested within the pilot (study 1, n = 3780) and main trial (study 2, n = 2667) phases of an evaluation of a Web-based intervention for hazardous drinkers: the Down Your Drink randomized controlled trial (DYD-RCT).  OBJECTIVES: The objective was to determine whether differences in the length and relevance of questionnaires can impact upon loss to follow-up in online trials.  METHODS: A randomized controlled trial design was used. All participants who consented to enter DYD-RCT and completed the primary outcome questionnaires were randomized to complete one of four secondary outcome questionnaires at baseline and at follow-up. These questionnaires varied in length (additional 23 or 34 versus 10 items) and relevance (alcohol problems versus mental health). The outcome measure was the proportion of participants who completed follow-up at each of two follow-up intervals: study 1 after 1 and 3 months and study 2 after 3 and 12 months.  RESULTS: At all four follow-up intervals there were no significant effects of additional questionnaire length on follow-up. Randomization to the less relevant questionnaire resulted in significantly lower rates of follow-up in two of the four assessments made (absolute difference of 4%, 95% confidence interval [CI] 0%-8%, in both study 1 after 1 month and in study 2 after 12 months). A post hoc pooled analysis across all four follow-up intervals found this effect of marginal statistical significance (unadjusted difference, 3%, range 1%-5%, P = .01; difference adjusted for prespecified covariates, 3%, range 0%-5%, P = .05).  CONCLUSIONS: Apparently minor differences in study design decisions may have a measurable impact on attrition in trials. Further investigation is warranted of the impact of the relevance of outcome measures on follow-up rates and, more broadly, of the consequences of what we ask participants to do when we invite them to take part in research studies.  TRIAL REGISTRATION: ISRCTN Register 31070347; Archived by WebCite at (

Item Type: Article
Faculty \ School: Faculty of Medicine and Health Sciences > School of Health Sciences
Depositing User: Pure Connector
Date Deposited: 09 Apr 2018 15:30
Last Modified: 22 Apr 2020 06:31
DOI: 10.2196/jmir.1733

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