Data extraction and quality assessment
Two independent reviewers (Y.L and D.C) extracted the data on
prespecified forms: authors, year of publication, study design, sample
size, research center, follow-up time, time of CRT implantation,
indication, adjusted covariates, endpoints and aHR value with its 95%
confidence interval (CI). When different adjusted models existed in one
study, we extracted the HR value with the greatest number of adjusted
confounding variables. In instances when incomplete data were obtained,
the authors were contacted in writing for permission to obtain further
data.
The quality of each study was assessed independently by the same two
investigators using the Newcastle-Ottawa scale (NOS), a nine-star scale
for nonrandomized study quality assessment in meta-analyses. Briefly,
this scale has three broad perspectives as follows: selection,
comparability and outcome of studies. Studies awarded more than six
stars were considered high-quality studies.