The Newcastle–Ottawa Scales were used to assess risk of bias for the cohort studies.

Abstract

Each domain was rated on a scale of zero or one star, except comparability, which can be awarded up to two stars. 0, High or unclear risk of bias; 1 or 2, low risk of bias (scores ≥ 7–9, 4–6, <4 are considered low, intermediate, and high risk, respectively).</p