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Table 3 Characteristics of the reference set

From: Study filters for non-randomized studies of interventions consistently lacked sensitivity upon external validation

Study type Number of CRsa) Number of studies Number of PMIDsb)
Randomized controlled trial 183 1471 1598
Nonrandomized controlled trial 67 216 331
Controlled before-after study 104 634 556
Interrupted time series (with comparison group) 31 83 106
Prospective cohort study 84 384 435
Retrospective cohort study 72 436 451
Non-concurrent cohort study 13 34 31
(Nested) case-control study 36 207 200
Cross-sectional study 17 152 136
Non-comparative study (case report or case series) 22 249 226
Before-after study 41 257 239
Interrupted time series (without comparison group) 45 221 179
Study type unclear 42 138 56
Total 271 4482 4544 (2890 on NRS)
  1. a)Number of CRs in which the study type was included at least once (multiple counting possible)
  2. b)Without duplicates