TABLE 1.

Study characteristics

Study characteristics		RCTs (N = 79)	Observational studies (N = 169)
Year of publication	1970–1979	1 (1.3%)	13 (7.7%)
	1980–1989	4 (5.1%)	17 (10.1%)
	1990–1999	15 (19.0%)	29 (17.2%)
	2000–2009	27 (34.2%)	61 (36.1%)
	2010–2019	32 (40.5%)	49 (28.9%)
Continent	Africa	6 (7.6%)	5 (3.0%)
	Asia	34 (43.0%)	41 (24.3%)
	Oceania	2 (2.5%)	6 (3.6%)
	Europe	20 (25.3%)	65 (38.5%)
	North America	11 (13.9%)	42(24.8%)
	South America	0	2 (1.2%)
	Multiple	6 (7.6%)	8 (4.7%)
Sample size	1–50	10 (12.7%)	32 (18.9%)
	51–100	19 (24.1%)	37 (21.9%)
	101–200	24 (30.4%)	33 (19.5%)
	201–500	13 (16.5%)	34 (20.1%)
	501–1000	7 (8.9%)	13 (7.7%)
	>1000	6 (7.6%)	20 (11.8%)

Abbreviation: RCT, randomized controlled trial.