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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