TABLE 2.
Associations between asthma and ADHD within individual and across relative cohorts
| Groups | Main analysis OR (95% CI) | Sensitivity analyses OR (95% CI) | ||
|---|---|---|---|---|
| Adjusting asthma | Adjusting ADHD | Asthma defined from NPR a | ||
| Within individual (n = 927,956) | 1.50 (1.47–1.54) | NA | NA | 1.57 (1.53–1.62) |
| MZ twins (n = 4956) | 1.67 (0.99–2.84) | 1.40 (0.90–2.20) | 1.38 (0.85–2.23) | 1.83 (0.99–3.41) |
| DZ twins (n = 18,140) | 1.29 (1.05–1.58) | 1.22 (1.00–1.50) | 1.21 (0.99–1.49) | 1.24 (0.98–1.58) |
| Full‐siblings (n = 625,888) | 1.39 (1.33–1.44) | 1.31 (1.26–1.36) | 1.30 (1.25–1.35) | 1.43 (1.36–1.49) |
| Maternal half‐siblings (n = 46,910) | 1.32 (1.21–1.44) | 1.26 (1.15–1.37) | 1.25 (1.15–1.37) | 1.37 (1.24–1.52) |
| Paternal half‐siblings (n = 43, 074) | 1.13 (1.02–1.24) | 1.10 (1.00–1.22) | 1.09 (0.99–1.20) | 1.16 (1.04–1.30) |
| Full‐cousins (n = 1,514,008) | 1.10 (1.07–1.13) | 1.09 (1.06–1.12) | 1.08 (1.06–1.11) | 1.13 (1.09–1.16) |
| Half‐cousins (n = 294,750) | 1.05 (1.00–1.10) | 1.04 (1.00–1.09) | 1.04 (0.99–1.08) | 1.05 (1.00–1.11) |
Note: In the main analysis, asthma was the exposure while ADHD was the outcome. Sex and year of birth for both the exposure and outcome person in the relative pairs were adjusted for. In the sensitivity analysis, asthma was furtherly adjusted for in the outcome person when asthma was the exposure variable; and ADHD was furtherly adjusted for in the outcome person when ADHD was the exposure variable.
Abbreviations: ADHD, attention‐deficit/hyperactivity disorder; CI, confidence interval; DZ, dizygotic twins; MZ, monozygotic twins; NPR, National Patient Register; OR, odd ratio.
Asthma was only defined by clinical diagnosis from NPR (ICD‐9 code 493 or ICD‐10 code J45–J46).