Table 4

Association between number of siblings and adult hay fever according to atopic status (serum specific IgE to grass, cat, house dust mite and/or mould) and parental allergy (mother and/or father having eczema, skin/nasal allergy, or hay fever ever).

Subgroups according to increasing number of predisposing factorsNo*No (%) with hay feverOR (95% CI)† per siblingp value
*Of 18 530 subjects who provided questionnaire information, 13 932 provided blood tests for IgE analyses and some data are missing for each variable. Thus, the totals of the individual rows does not equal the final total.
†Estimated by logistic regression adjusted for number of siblings, bedroom sharing, serious respiratory infections, sex, age, current smoking, current occupation, and centre.
No atopy, no parental allergy6852839 (12%)1.02 (0.97 to 1.09)NS
No atopy, parental allergy2508603 (24%)0.91 (0.84 to 0.99)0.028
Atopy, no parental allergy29081176 (40%)0.92 (0.86 to 0.98)0.007
Atopy, parental allergy15811021 (64%)0.88 (0.80 to 0.96)0.006
All176764840 (27%)0.92 (0.90 to 0.95)<0.001