Data extraction
Initially, at least two authors (XSY, NSM, and ZCL) independently screened the records on titles and abstracts. Any relevant studies were included for full-text assessment. Duplicates were removed if the same study population was presented in different publications, and the publication with the most comprehensive dataset was included. If there are overlaps of study population in different publications and different parts could fit into various analyses, both publications were included. The following data were collected: author, publication year, age, sex, study design, assessment of rhinitis and urticaria, number of patients in total, number of rhinitis patients, number of rhinitis patients with urticaria, number of controls, number of controls with urticaria, number of urticaria patients, number of urticaria patients with rhinitis, and number of controls with rhinitis. Detailed extracted data of all included studies are presented in Supplementary Table 2. All steps of data extraction were performed by at least two authors, and any potential disagreements were resolved by a reviewer (PYJ).