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Table 1 Basic characteristics of included systematic reviews on adverse events

From: Utilization of the evidence from studies with no events in meta-analyses of adverse events: an empirical investigation

Basic characteristics No. of systematic reviews (N = 640)
Year
 2008–2011 184 (28.75%)
 2015–2020 456 (71.25%)
Region of corresponding author
 Africa 15 (2.34%)
 America (North and South) 193 (30.16%)
 Asia 193 (30.16%)
 European 219 (34.22%)
 Oceania 20 (3.13%)
Intervention
 Drug 483 (75.47%)
 Surgery or device 108 (16.88%)
 Others (e.g., complementary medicine) 49 (7.66%)
Type of meta-analysis
 Pairwise meta-analysis 585 (91.41%)
 Network meta-analysis 17 (2.66%)
 Both pairwise and network meta-analyses 32 (5.0%)
 Association 2 (0.31%)
 Individual participant data 4 (0.63%)
Protocol
 Yes 166 (25.94%)
 No 474 (74.06%)
Type of study for meta-analysis
 Randomized controlled trial (RCT) 460 (71.88%)
 Non-randomized study of intervention (NRSI) 89 (13.91%)
 Both RCT and NRSI 87 (13.59%)
 Not reported 4 (0.63%)
Effect estimator
 Odds ratio, including Peto’s OR 266 (41.56%)
 Risk ratio or relative risk 316 (49.38%)
 Hazard ratio 9 (1.41%)
 Risk difference 15 (2.34%)
 Others (e.g., mixed use, Chi2, coef.) 34 (5.31%)
Systematic review with zero-events studies in meta-analysis
 Yes 406 (63.45%)
 No 88 (13.75%)
 No data available for judgment 146 (22.80%)
Power analysis
 Yes 16 (2.50%)
 No 624 (97.5%)