Table 3.

Results of the Newcastle-Ottawa Scale (NOS) [9] performed for the four cohort studies.

Author(s)	Cohort Studies	Selection				Comparability	Outcomes			Total of nine scores
		1	2	3	4	(∗∗)	1	2	3
Hernandez-Romieu et al. [7]	Multi-center, Retrospective	N	∗	∗	∗	∗∗	∗	∗	∗	8
Mellado-Artigas et al. [8]	Multi-center, Prospective	∗	N	∗	∗	∗∗	∗	∗	∗	8
Pandya et al. [5]	Single-center, Retrospective	∗	∗	∗	∗	∗∗	∗	∗	∗	9
Vera et al. [6]	Single-center, Prospective	∗	∗	∗	∗	∗∗	∗	∗	∗	9

1. Representatives of exposed cohorts.

2. Selection of non-exposed cohorts.

3. Ascertainment of exposure.

4. Outcome of interest not present at the start of the study.

Comparability: Study controls are compared for the most important factor and additional factors.

a) Assessment of outcome.

b) Enough follow-up for outcome.

c) Adequacy of follow-up.

Abbreviations: ∗, positive variable; N, negative variable.