@Article{info:doi/10.2196/jmir.1733,
author="McCambridge, Jim
and Kalaitzaki, Eleftheria
and White, Ian R
and Khadjesari, Zarnie
and Murray, Elizabeth
and Linke, Stuart
and Thompson, Simon G
and Godfrey, Christine
and Wallace, Paul",
title="Impact of Length or Relevance of Questionnaires on Attrition in Online Trials: Randomized Controlled Trial",
journal="J Med Internet Res",
year="2011",
month="Nov",
day="18",
volume="13",
number="4",
pages="e96",
keywords="Attrition; retention; missing data; response rates; alcohol; online",
abstract="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; http://www.controlled-trials.com/ISRCTN31070347/31070347 Archived by WebCite at (http://www.webcitation.org/62cpeyYaY) ",
issn="1438-8871",
doi="10.2196/jmir.1733",
url="http://www.jmir.org/2011/4/e96/",
url="https://doi.org/10.2196/jmir.1733",
url="http://www.ncbi.nlm.nih.gov/pubmed/22100793"
}