Table 2.

Critical appraisal of the included systematic review

Author; year	Study design	Validity					Importance			LOEa,b,c
		PICO	F	A1	A2	T	Outcome	Estimates [95% CI]	Heterogeneity
Kow CS; 2020 [7]	SR of cohort studies	✓	✗	✓	✓	✓	Mortality	OR 0.62 [0.43–0.89]	I2 = 29%; p = 0.23	IId,e

^aLOE of evidence may be upgraded by one level due to large effect size (RR > 2 or RR < 0.5) or by two level due to very large effect size (RR > 5 or RR < 0.2). ^bLOE may be downgraded by one level each due to imprecision (wide CI: upper limit – lower limit of 95% CI > 1 [for increased risks] or > 0.8 [for decreased risks]), indirectness (study PICO not applicable to question’s PICO), inconsistency (I² > 50% or p < 0.10), and poor study quality (validity score < 4). ^cLOE may be downgraded by two levels each due to very serious imprecision (very wide CI: upper limit – lower limit of 95% CI > 5 [for increased risks] or > 0.5 [for decreased risks]), very serious inconsistency (I² > 75% or p < 0.01), or very poor study quality (validity score < 2). ^dLOE assessment starts with level III. ^eUpgraded by one level due to systematic review design

✓, no serious limitation; ✗, serious limitation; PICO, clear statement of review question; F, comprehensive strategy to find eligible studies; A1, appropriate eligibility criteria; A2, appropriate risk of bias or methodological quality assessment; T, appropriate strategy to total up the summary of findings; CI, confidence interval; I², I-squared value; LOE, level of evidence; OR, odds ratio; SR, systematic review