Table 3.

Newcastle–Ottawa Scale quality assessment of studies included in the systematic review

References	Rossi et al. [22]	Chan et al. [4]	Chan et al. [5]	Gill et al. [8]	Lobenhoffer et al. [15]	Siegler et al. [24]	Kayali et al. [12]	Duan et al. [6]	Pogliacomi et al. [19]	Asik et al. [1]	Glabbeek et al. [26]	Roerdink et al. [21]
Selection
(1) Representativeness of the exposed cohort
(a) Truly representative of the average patient in the community
(b) Somewhat representative of the average patient in the community	*	*	*		*	*	*	*	*	*	*
(c) Selected group of users, e.g., nurses, volunteers				*								*
(d) No description of the derivation of the cohort
(2) Selection of the non-exposed cohort	NA	NA	NA	NA		NA	NA	NA	NA	NA	NA	NA
(a) Drawn from the same community as the exposed cohort
(b) Drawn from a different source					*
(c) No description of the derivation of the non-exposed cohort
(3) Ascertainment of exposure
(a) Secure record (e.g., surgical records)	*	*	*	*	*	*	*	*	*	*	*	*
(b) Structured interview
(c) Written self-report
(d) No description
(4) Demonstration that outcome of interest was not present at start of study
(a) Yes	*	*	*	*	*	*	*	*	*	*	*	*
(b) No
Comparability
(1) Comparability of cohorts on the basis of the design or analysis
(a) Study controls for scores	*	*	*	*	*	*	*	*	*	*	*	*
(b) Study controls for any additional factor
Outcome
(1) Assessment of outcome
(a) Independent blind assessment
(b) Record linkage	*	*	*	*	*	*	*	*	*	*	*	*
(c) Self-report
(d) No description
(2) Was follow-up long enough for outcomes to occur
(a) Yes (select an adequate follow-up period for outcome of interest)	*	*	*	*	*	*	*	*	*	*	*	*
(b) No
(3) Adequacy of follow-up of cohorts
(a) Complete follow-up—all subjects accounted for	*	*	*	*			*	*	*	*	*	*
(b) Subjects lost to follow-up unlikely to introduce bias					n = 7*	25%*
(c) Follow-up rate and no description of those lost
(d) No statement

NA not applicable

* means yes