Data extraction and risk of bias assessment
The items of each eligible study were extracted by two reviewers (Zhou
and Li), including the first author, year of publication, year of
investigation, study settings, research type, study population, sample
size, definition of infertility, and prevalence of infertility and
subtypes (primary and secondary). In parallel, the two reviewers
assessed the relevant studies using the 10-item Hoy risk of bias tool
(Table S2), designed for prevalence studies. Each item was rated on a
dichotomous scale, with 1 indicating low risk of bias and 0 indicating
high risk of bias. An overall score was calculated for each study as the
mean score of the two reviewers, ranging from 0 to 10, with a score of
at least 9 indicating a low risk of bias, 7–8 indicating a moderate
risk, and less than 7 indicating a high risk.
We calculated inter-rater
reliability using the kappa coefficient for each item (Table S3).