Table 1

Newcastle-Ottawa Quality Assessment Scale criteria

Study	Selection				Comparability	Outcomes			Total
Study	Representativeness of exposed cohort	Selection of non-exposed cohort	Ascertainment of exposure	Outcome not present at the start of the study	Comparability of cohorts	Assessment of outcomes	Length of follow-up	Adequacy of follow-up	Quality score
Bjørneboe et al35	*	*	*	–	**	*	*	n/a	Good
Ekstrand et al36	*	*	*	*	**	*	*	n/a	Good
Fuller et al30	*	*	–	*	**	*	*	n/a	Good
Fuller et al31	*	*	–	*	**	*	*	n/a	Good
Kordi et al37	*	*	–	–	*	*	–	n/a	Poor
Kristenson et al4	*	*	*	*	**	*	*	n/a	Good
Meyers and Barnhill33	*	*	*	*	**	*	*	n/a	Good
Meyers27	*	*	*	*	**	*	*	n/a	Good
Meyers28	*	*	*	*	**	*	*	n/a	Good
Meyers29	*	*	*	*	**	*	*	n/a	Good
Ranson et al32	*	*	–	*	**	*	*	n/a	Good
Soligard et al38	–	–	–	*	**	–	*	n/a	Poor

Thresholds for converting the Newcastle-Ottawa Scales to AHRQ standards (good, fair and poor).
Good quality: three or four stars in selection domain and one or two stars in comparability domain and two or three stars in outcome/exposure domain.
Fair quality: two stars in selection domain, and one or two stars in comparability domain and two or three stars in outcome/exposure domain.
Poor quality: zero or one star in selection domain or zero stars in comparability domain or zero or one star in outcome/exposure domain.
AHRQ, Agency for Healthcare Research and Quality; n/a, not applicable.