Quality assessment
Risk of bias was assessed using the Cochrane Collaboration’s tool
addressing six domains: sequence generation, allocation concealment,
blinding of participants/outcome assessors, incomplete outcome,
selective outcome reporting and other source of bias. These articles are
almost non-randomized controlled (NRCT) studies, so the Newcastle Ottawa
scale (NOS) recommended by Cochrane Collaboration Network is used to
evaluate the quality of retrospective cohort studies.