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Table 1 Algorithm for categorizing the “main” outcome domain for each systematic review

From: Outcome choice and definition in systematic reviews leads to few eligible studies included in meta-analyses: a case study

ScenarioIfThenNumber of systematic reviews (N = 175)
n (%)
1The review named only 1 primary outcome domainwe categorized that outcome domain as the main outcome domain.131 (75)
2The review named >1 primary outcome domainwe categorized the primary outcome domain with the highest number of included studies as the main outcome domain.41 (23)
3The review did not name any primary outcome domain, but named ≥1 secondary outcome domainwe categorized the secondary outcome domain with the highest number of included studies as the main outcome domain.0 (0)
4If the review did not name any primary or secondary outcome domainswe categorized the “other” (i.e., non-primary and non-secondary) outcome domain with the highest number of included studies as the main outcome domain.3 (2)
  1. Note
  2. In scenarios 2, 3, and 4, if there were two or more possible outcome domains that had the same number of included studies (“Then” column), we categorized the first outcome listed in the Methods section as the main outcome domain