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.

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.