Table 4. Results of mixed-effects, multivariate, logistic regression analysis: association between study validity and country income, sample size, year and language of publication.

	Odds ratio (95% CI)	P-value
Middle-income country (1 for middle-income country; 0 for high-income country)	0.444 (0.251, 0.786)	0.005
Multiple-income countries (1 for mixed-income; 0 for high-income country)	1.987 (0.856, 4.609)	0.110
Sample size (1 for sample size ≥200; 0 for sample size <200)	2.643 (1.751, 3.988)	<0.001
Year of publication (1 for published since 2005; 0 for published before 2005)	3.173 (2.123, 4.743)	<0.001
Published in English (1 for English; 0 for non-English)	5.532 (1.892, 16.178)	0.002

Note: Dependent variable is defined as at least 4 of the 5 quality items being low risk of bias.