Table 3.

Meta-regression analysis for the included studies to identify the sources of heterogeneity.

Variables	Category	Coef.	Std. err.	t	p < |t|	(95% conf. interval)
By year of publication	Before 2010(reference)	0.421	1.106	0.38	0.771	(−2.043 to 2.88)
	2010 and above
Sample size	<300 (reference)	−0.041	0.487	−0.08	0.934	(−1.126 to 1.044)
	≥300
Sampling technique	Systematic	0.614	1.267	0.51	0.628	(−2.35 to 3.63)
	Simple random	0.254	1.85	0.14	0.895	(−4.13 to 4.64)
	Consecutive	0.202	1.219	0.17	0.873	(−2.68 to 3.08)
	Not specified (reference)