A marked seasonality of births for the two main ethnic groups of peninsular Malaysia, far exceeding the cyclic fluctuations in births in the United States and Canada, was reported for the 1960s. A 36% excess of births over the average monthly number was observed among Malays each January. Among the ethnic Chinese in Malaysia a regular periodicity in the numbers of births was also found, but it was far less marked and the peak occurred in October or November. The peaks in both groups were due in large measure to conceptions that correlate with religious observances or holidays. Here I report on cyclic birth patterns in peninsular Malaysia for the period 1970-1985. Rapid economic development has occurred during this time and has brought with it demographic changes, such as a massive rise in contraceptive use and a decline in birth rates. These demographic changes have been accompanied by the loss of the pronounced seasonal pattern of births among the Malays. The seasonality of Malay births is now of roughly the same magnitude as the seasonality in the United States and Canada, whereas seasonality of births among the Chinese in Malaysia remains essentially unchanged.
The effects of breast-feeding on infant health and mortality, particularly in the developing nations, are a matter of controversy and importance. The Malaysian Family Life Survey (MFLS) of over 1200 women has recently been the source of a great deal of valuable information on the influence of breast-feeding and interacting social variables on the incidence of infant mortality. Accuracy of reporting of breast-feeding duration is a key issue in the validity of studies of breast-feeding and infant mortality. This paper presents an illustrative analysis of the quality of breast-feeding data from the Malaysian Family Life Survey, using logit model schedules. Lesthaeghe and Page derived a logit model schedule of breast-feeding, summarizing empirical experience. This family of model breast-feeding duration curves is similar to the logit model life tables developed by Brass, and was intended for similar applications. To verify the MFLS retrospective breast-feeding reports, the observed median duration and variability were calculated for ethnic group/cohort subsets, and expected duration distribution curves were generated from the model using these observed parameter values. The expected curve generated from the model fit the observed curve of breast-feeding discontinuation extremely closely. Thus it is unlikely that any significant distortion of the pattern of discontinuation of breast-feeding occurred in data collection. Extensions of this method of data quality checking to other duration distributions are suggested.