Table 2.

Assessment of quality across studies.

Study	Quality score (Newcastle-Ottawa Quality Assessment Scale)a
Ding et al.39	Selection ***	Comparability **	Outcome ***
Ngo et al.46	Selection ***	Comparability **	Outcome ***
Bournival et al.47	Selection ***	Comparability **	Outcome ***
Liang et al.48	Selection ***	Comparability **	Outcome ***
Molimard et al.22	Selection ****	Comparability **	Outcome ***
Takaku et al.49	Selection ***	Comparability **	Outcome ***
Chorao et al.42	Selection ***	Comparability **	Outcome ***
Steinberg and Pervanas44	Selection ***	Comparability **	Outcome ***
Asakura et al.43	Selection ***	Comparability **	Outcome **
	Quality score (GRADE)b
Oliveira et al.40	++++ High
Windisch et al.45	++ Low
Ohbayashi et al.41	+++ Moderate

^a Scale used to assess quality rating in observational studies; Good quality: three or four stars (*) in selection domain, one or two stars in the comparability domain, and two or three stars in the outcome domain; Fair quality: two stars in the selection domain, one or two stars in the comparability domain, and two or three stars in the outcome domain; Poor quality: zero or one star in the selection domain/zero stars in the comparability domain/zero or one star in the outcome domain.

^b Scale used to assess quality rating in randomized controlled trials; High: We were confident that the true effect lied close to that of the estimate of the effect; Moderate: We were moderately confident in the effect estimate: The true effect was likely to be close to the estimate of the effect, but there was a possibility that it was substantially different; Low: Our confidence in the effect estimate was rather limited, the true effect may have been substantially different from the estimate of the effect.