Table 3

 Association of sibship size and birth order with prevalence of allergy by three periods of birth

CrudePartially adjusted*Fully adjusted†
OR95% CIptrendOR95% CIptrendOR95% CIptrend
OR, odds ratio; 95% CI, 95% confidence intervals.
*Adjusted for age, sex, year of birth, year of examination, and family history of allergy.
†Adjusted for sibship size, birth order, childhood socioeconomic position, age, sex, year of birth, year of examination, and family history of allergy.
Interaction tests for fully adjusted models: (a) sibship size and period of birth, p = 0.554; (b) birth order and period of birth, p = 0.209.
Born 1918–1930
Sibship size
    0111
    10.75(0.56 to 0.99)0.72(0.54 to 0.96)0.76(0.56 to 1.02)
    20.59(0.43 to 0.82)0.58(0.42 to 0.80)0.64(0.45 to 0.93)
    3+0.52(0.38 to 0.72)<0.0010.49(0.35 to 0.67)<0.0010.57(0.38 to 0.85)0.006
Birth order
    1111
    20.67(0.52 to 0.86)0.68(0.52 to 0.87)0.76(0.58 to 1.00)
    3+0.63(0.47 to 0.83)<0.0010.62(0.47 to 0.83)<0.0010.87(0.60 to 1.25)0.202
Born 1931–1939
Sibship size
    0111
    10.92(0.74 to 1.14)0.84(0.67 to 1.04)0.86(0.68 to 1.07)
    20.85(0.67 to 1.09)0.76(0.59 to 0.98)0.80(0.61 to 1.05)
    3+0.77(0.60 to 1.00)0.0410.69(0.53 to 0.90)0.0100.77(0.57 to 1.05)0.095
Birth order
    1111
    21.00(0.82 to 1.21)0.92(0.76 to 1.12)0.96(0.78 to 1.18)
    3+0.74(0.58 to 0.95)0.0390.71(0.55 to 0.91)0.1780.83(0.62 to 1.12)0.262
Born 1940–1952
Sibship size
    0111
    10.90(0.71 to 1.13)0.85(0.67 to 1.08)0.86(0.67 to 1.10)
    20.89(0.69 to 1.15)0.80(0.62 to 1.03)0.82(0.62 to 1.09)
    3+0.79(0.60 to 1.05)0.1290.70(0.53 to 0.93)0.0670.74(0.54 to 1.01)0.066
Birth order
    1111
    21.00(0.82 to 1.20)0.98(0.81 to 1.19)1.03(0.84 to 1.25)
    3+0.78(0.60 to 1.01)0.1060.76(0.58 to 0.98)0.1780.86(0.64 to 1.16)0.488