Table 4.

Quality assessment of the 37 selected studies with the NHLBI tool [32].

Criteria	Score	Maximum Score	%
Was the research question or objective in this paper clearly stated?	37	37	100
Was the study population clearly specified and defined?	36	37	97.3
Was the participation rate of eligible persons at least 50%?	24 **	37	64.9 *
Were all the subjects selected or recruited from the same or similar populations (including the same time period)?	18.5	18.5	100
Were inclusion and exclusion criteria for being in the study prespecified and applied uniformly to all participants?	18.5	18.5	100
Was a sample size justification, power description or variance and effect estimate provided?	25	37	67.6 *
Were the exposure measures (independent variables) clearly defined, valid, reliable and implemented consistently across all study participants?	37	37	100
Was the exposure(s) assessed more than once over time? (i.e., Was the questionnaire administered at least two times in different moments?/exposure or evaluation of independent variable)	2	18.5	10.8 *
Was loss to follow-up after baseline 20% or less? (i.e., % of participants who did not reply to the second questionnaire)	1	18.5	5.4 *
Were the outcome measures (dependent variables) clearly defined, valid, reliable and implemented consistently across all study participants?	37	37	100
Were key potential confounding variables measured and adjusted statistically for their impact on the relationship between exposure(s) and outcome(s)?	37	37	100
Was loss to follow-up after baseline 20% or less?	37	37	100

* Poor scores (below 80%); ** the participation rate was not reported in 20 out of the 37 studies.