The use of logit models to investigate social and biological factors in infant mortality. II: Stillbirths.

Infant mortality data for England and Wales cross-classified by mother's age, parity and social class have only been published for 1949/50 and 1975. Appropriate statistical methodology for the analysis of such data has been described in Paper I, which used the 1975 stillbirth data for illustration. This paper examines the stillbirth data from both years by formally incorporating the year of data collection into the statistical model, enabling changes in the age, parity and social class effects with time to be investigated. Despite a marked reduction in stillbirth mortality from 21.1 to 10.1 per thousand over the period, the relative contribution of social class has increased. In particular there has been a relative increase in risk for mothers in the lower social classes. By contrast the effects of age and parity, although remaining important, have diminished over the period.