Reducing bias in trials due to reactions to measurement: experts produced recommendations informed by evidence  

David P French* (Corresponding Author), Lisa M. Miles, Diana R. Elbourne, Andrew J. Farmer, Martin C. Gulliford, Louise Locock, Stephen Sutton, Jim McCambridge, MERIT Collaborative group

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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This study (MEasurement Reactions In Trials) aimed to produce recommendations on how best to minimise bias from measurement reactivity in randomised controlled trials of interventions to improve health.
Study design and setting:
The MERIT study consisted of: (a) an updated systematic review that examined whether measuring participants had effects on participants’ health-related behaviours, relative to no-measurement controls, and three rapid reviews to identify: (i) existing guidance on measurement reactivity; (ii) existing systematic reviews of studies that have quantified the effects of measurement on
behavioural or affective outcomes; and (iii) studies that have investigated the effects of objective measurements of behaviour on health-related behaviour; (b) an Delphi study to identify the scope of the recommendations; and (c) an expert workshop in October 2018 to discuss potential recommendations in groups.
Fourteen recommendations were produced by the expert group to: (a) identify whether bias is likely to be a problem for a trial; (b) decide whether to collect data about whether bias is likely to be a problem; (c) design trials to minimise the likelihood of this bias.
These recommendations raise awareness of how and where taking measurements can produce bias in trials, and are thus helpful for trial design.
Original languageEnglish
Pages (from-to)130-139
Number of pages10
JournalJournal of Clinical Epidemiology
Early online date3 Jul 2021
Publication statusPublished - 30 Nov 2021

Bibliographical note

The authors would like to acknowledge the expert input provided into the scope of these recommendations from participants in an international Delphi procedure. The following people took part in the Delphi procedure and participants had a range of views. Participation in the Delphi procedure does not necessarily mean agreement with the recommendations
The MERIT study was funded by the MRC/NIHR Methodology Research Programme (reference MC_PC_17229); funders have had no role in the design of the study or the writing of this manuscript. The work of RD and AL (members of MERIT Collaborative Group) is funded by the Medical Research Council (MC_UU_12017/13) and the Scottish Government Chief Scientist Office (SPHSU13).


  • Bias
  • measurement reactions
  • Reactivity
  • Recommendations
  • Research Design
  • trials


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