Study screening and data extraction
Retrieved articles were independently screened according to titles and
abstracts by two reviewers. Any discrepancy was resolved by discussion.
The same process was employed for full-text screening. The full texts
were assured by cross checking by consensus for validation and accuracy.
The following data as the characteristics of various studies was
extracted from eligible studies: first author’s name, publication year,
research design, sample size, country, type of allergic diseases in the
children, effect estimates (odds ratios, hazard ratios, risk ratios or
prevalence ratios) and 95% confidence interval. All data was imported
to Excel for analysis.