Table 2.

Quality assessment of included observational cohort and cross-sectional studies according to NHBLI Quality Assessment Tool

	Hwang et al[10], 2014	Hassan et al[9], 2014	Karvellas et al[11], 2015	Bremmer et al[1], 2015	Lahmer et al[2], 2016
1 Was the research question or objective in this paper clearly stated?	Yes	Yes	Yes	Yes	Yes
2 Was the study population clearly specified and defined?	Yes	Yes	Yes	Yes	Yes
3 Was the participation rate of eligible persons at least 50%?	Yes	Yes	Yes	Yes	Yes
4 Were all the subjects selected or recruited from the same or similar populations (including the same time period)? Were inclusion and exclusion criteria for being in the study prespecified and applied uniformly to all participants?	Yes	Yes	Yes	Yes	Yes
5 Was a sample size justification, power description, or variance and effect estimates provided?	No	No	No	No	No
6 For the analyses in this paper, were the exposure(s) of interest measured prior to the outcome(s) being measured?	Yes	Yes	Yes	Yes	Yes
7 Was the timeframe sufficient so that one could reasonably expect to see an association between exposure and outcome if it existed?	Yes	Yes	Yes	Yes	Yes
8 For exposures that can vary in amount or level, did the study examine different levels of the exposure as related to the outcome (e.g., categories of exposure, or exposure measured as continuous variable)?	NA	NA	Yes	NA	NA
9 Were the exposure measures (independent variables) clearly defined, valid, reliable, and implemented consistently across all study participants?	Yes	Yes	Yes	Yes	Yes
10 Was the exposure(s) assessed more than once over time?	No	No	No	No	No
11 Were the outcome measures (dependent variables) clearly defined, valid, reliable, and implemented consistently across all study participants?	Yes	Yes	Yes	Yes	Yes
12 Were the outcome assessors blinded to the exposure status of participants?	No	No	No	No	No
13 Was loss to follow-up after baseline 20% or less?	Yes	Yes	Yes	Yes	Yes
14 Were key potential confounding variables measured and adjusted statistically for their impact on the relationship between exposure(s) and outcome(s)?	No	Yes	Yes	Yes	Yes
Rating	Good	Good	Good	Good	Good