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Table 3 Exposure and outcome assessment of included studies by year and author

From: Childhood body mass index and subsequent physician-diagnosed asthma: a systematic review and meta-analysis of prospective cohort studies

Study Obesity (exposure measure) Asthma (outcome measure) Confounder assessment Subgroup analysis Statistical methods
Gilliland et al., 2003 [45] Not overweight: ≤85th% vs. Overweight: >85th%; New-onset physician diagnosed Asthma (child-report) Age, sex, race, health insurance, community, parental history of asthma/allergies, birth weight, humidifier use, wheeze, allergy, team sports participation, smoking, household ETS, household pets and pests, puberty, and lung function Sex Cox proportional hazards
Not obese: ≤95th% vs. obese: >95th%
Gold et al., 2003 [46] BMI by Z-score New-onset doctor diagnosed Asthma with wheeze (parental-report) Maternal smoking, air conditioner use, city of residence, child’s exact age, parental education level, single-parent household, only child status, and race Sex, race, maternal smoking, age Cox proportional hazards from BMI Z-score modeled as a time-dependent variable
BMI by Quintile annual updated BMI Z-scores included as a time-dependent variable
Mamun et al., 2007 [47] BMI by Z-score at age 5 and 14 years Asthma at ages 5 years (maternal-report) and age 14 years (self-report)   Sex One-way ANOVA and F-test used for association between BMI and asthma; logistic regression
Mannino et al., 2006 [48] Underweight: <25th% New-onset asthma that limited child’s activity or required the use of medication or frequent attention from a doctor (parental-report) Race/ethnicity, sex, poverty status, birthweight, and prenatal maternal smoking Sex Cox proportional hazards models
Normal weight: 25th-84th%
Overweight/obese: ≥85th%
Zhang et al., 2010 [49] Age 3 years: Incident asthma at age 6 years Breast-feeding, sex, self-reported maternal asthma, dog and cat in household at birth, smoke exposure, day care attendance, having older children in household, and wheezing with rhinovirus infection. Asthma at 6 years old, asthma at 8 years old Logistic regression
Low weight: <15th%
Average weight: 15th-84th%
High weight: >85th%
Age 5 years: Incident asthma at age 8 years
Low weight: <15th%
Average weight: 15th-84th%
High weight: >85th%
Ho et al., 2011 [50] Underweight New-onset physician diagnosed Asthma (self-report and parental-report) Exercise, parental asthma, parental education, breastfeeding, air-conditioning usage, cigarette smoking, ETS, pet(s), and fungus/mold in the home Sex Mantel-Haenszel chi-square; Multivariable logistic regression
Normal weight