Despite the methodological frailty of observational studies, it
is worth noting again that RCT are not suitable for this type of
research for ethical reasons. The limitations of this study design
can be compensated by its methodological quality as assessed
by the Newcastle-Ottawa Scale. This scale focus on 3 pillars
to assess: 1) patient selection (including representativeness of
the exposed cohort, non-exposed cohort selection, exposure
ascertainment and demonstration that the outcome of interest
was not present at start of study), 2) cohorts comparability
on the basis of design or analysis, and 3) outcome (including
outcome assessment, whether follow-up was long enough
for outcome and cohort follow-up adequacy) (16). A total of
9 stars could be attributed to the studies; if they counted for
more than 6 stars, they were considered to be good quality (17).
Table 1 presents the methodological quality assessment of the
considered articles; one may conclude that 78% (7 in 9) of the
publications presented a satisfactory evaluation.