Table 3.

Newcastle–Ottawa Scale (NOS) scores for the included studies

	Selection score	Comparability score	Exposure/Outcome score	Overall score
Owusu et al. 2013	2/5	2/2	2/3	6/10
Lakshmi et al. 2017	1/4	0/2	0/3	1/9

NOS adapted for cross-sectional studies was used for the Owusu et al. study

Maximum scores: selection = 5, comparability = 2, outcome = 3, and overall = 10

High risk of bias: score ≤ 3

Medium risk of bias: score 4–7

Low risk of bias: score ≥ 8

The traditional NOS tool was used for the Lakshmi et al. study

Maximum scores: selection = 4, comparability = 2, exposure = 3 and overall = 9

High risk of bias: score ≤ 3

Medium risk of bias: score 4–6

Low risk of bias: score ≥ 7