Many scenarios exist for selective inclusion and reporting of results in randomized trials and systematic reviews

Objective: To collate and categorize the ways in which selective inclusion and reporting can occur in randomized controlled trials (RCTs) and systematic reviews.

Study design and setting: Searches of the Cochrane Methodology Register, PubMed, and PsycInfo were conducted in April 2011. Methodological reports describing empirically investigated or hypothetical examples of selective inclusion or reporting were eligible for inclusion. Examples were extracted from the reports by one author and categorized by three authors independently. Discrepancies in categorization were resolved via discussion.

Results: Two hundred ninety reports were included. The majority were empirical method studies (45.5%) or commentaries (29.3%). Eight categories (30 examples) of selective reporting in RCTs, eight categories (27 examples) of selective inclusion in systematic reviews, and eight categories (33 examples) of selective reporting in systematic reviews were collated. Broadly, these describe scenarios in which multiple outcomes or multiple data for the same outcome are available, yet only a subset is included or reported; outcome data are reported with inadequate detail; or outcome data are given different prominence through its placement across or within reports.

Conclusion: An extensive list of examples of selective inclusion and reporting was collated. Increasing trialists' and systematic reviewers' awareness of these examples may minimize their occurrence.