Siblings, asthma, rhinoconjunctivitis and eczema: a worldwide perspective from the International Study of Asthma and Allergies in Childhood.

Highly significant ( P < 0.0001) trends of lower prevalence with increasing sibship size were observed in both age groups for a lifetime history of hay fever and for a lifetime history of eczema, with a less significant ( P < 0.001) trend for asthma ever in the adolescents, but not for asthma ever in the younger age group.

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Although current symptoms were generally not significantly associated with sibship size, the exception was current flexural dermatitis which showed a trend ( P < 0.01) to be more common in larger families.

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