Methods: A comprehensive search, using a combination of free text words and MeSH subject headings was run in 4 databases (MEDLINE, CINHAL, EMBASE, PsycINFO), from the commencement of each database until June 2013, with no restriction on study design or language. We searched for published and unpublished studies, contacted experts, and conducted forward and backward citation searching of included studies. Studies were eligible if they assessed participants’ expectations of the benefits and/or harms of a treatment, test, or screen, and required participants to provide a quantitative estimate of the benefit and/or harm. Screening of search results, risk of bias assessment, and data extraction of eligible articles were conducted by two independent assessors, with disagreements resolved by discussion and a third assessor as needed.
Results: We screened 15 343 records and 32 studies, involving a total of 24 126 participants, were eligible: 14 studied screening, 13 a treatment, 3 a diagnostic test, and 2 studied both screening and treatments. Participants’ expectations of the benefit of the focus intervention were assessed by 29 studies, of which 25 compared participants’ quantitative estimates with a ‘correct’ (based on published research at the time of the study) estimate of the benefit of the intervention. All 25 studies found that patients over-estimated the intervention benefit. Ten studies assessed participants’ expectations about the harm of the focus interventions of which 8 compared participants’ quantitative estimates with a ‘correct’ estimate of the harm. In 7 of these, most participants underestimated the harms of the intervention.
Conclusions: Patients generally over-estimate intervention benefit, and underestimate intervention harm, with this finding consistent across a range of treatments, tests, and screening tests. These findings reinforce the importance of undertaking shared decision making when any intervention is being considered, including eliciting patients’ expectations, and ensuring that patients have the opportunity to make an informed decision.