... effect of birth order isalreadypresentatthetimeofbirthofthechild,then the effect of hygiene later in childhood may not be asrelevant as is currently thought. In support of this expla-nat ion, othe ... investigation, the hygiene hypothesis may explain observed associationsbetween family size, birth order, day-care attendance,and the risk of asthma and allergy. According to the hygiene concept, the effect ... estimated the effect of IL13 polymor-phisms using the dominant model, i.e. the heterozygousgenotype was combined with the homozygous minorallele genotype in one category, while the homozygouscomm...