The effects of infant feeding, birth order, occupation and socio-economic status on speech in six-year-old children.

The relationship of breast-feeding to the incidence of clear speech at six years of age was examined for 319 New Zealand children of European descent in samples from Putaruru and West Coast. Children were more likely to be breast-fed if first-born, and less likely if the father's occupational group was business or labouring. Differences in clear speech were associated with birth order and socio-economic status. Controlling for these effects, the association of breast-feeding with clear speech was different for the sexes. It was negligible for girls but strongly positive for boys.