Variability of birth-weight distributions by sex and ethnicity: analysis using mixture models.

Birth weight is the most important proximate determinant of the level of infant mortality. However, the association between birth weight and infant mortality is not constant among populations. For example, the mortality of African American infants is lower at low birth weight but higher at high birth weight compared with European American infants. One possible explanation is that birth cohorts are heterogeneous even after controlling for birth weight, ethnicity, sex, and multiple births. The analyses presented here use Gaussian mixture models to explore the interpopulation variation in the shape of the birth-weight distribution for evidence of intrapopulation heterogeneity. The results suggest that a two-component mixture model provides an excellent description of human birth-weight distributions. Further statistical analyses of sex and ethnic differences indicate (1) that the birth-weight distributions and heterogeneity within the distribution vary between the sexes and among ethnic groups and (2) that one specific component is more closely associated with the overall level of infant mortality. The results support the hypothesis that birth cohorts can consist of two or more subpopulations at differential risk of mortality. Differences in the subpopulation composition of birth cohorts (i.e., differences in the level of heterogeneity among the various ethnic groups) might partially explain the interethnic variation in birth-weight-specific mortality. Further development of these mixture models should provide important additional information concerning the biological, environmental, and social determinants of birth weight and infant mortality.

Hospital volume differences and five-year survival from breast cancer.

OBJECTIVES: The purpose of this study was to determine the effect of hospital volume on long-term survival for women with breast cancer. METHODS: Survival analysis and proportional-hazard modeling were used to assess 5-year survival and risk of death, adjusting for clinical and sociodemographic variables. RESULTS: At 5 years, patients from very low-volume hospitals had a 60% greater risk of all-cause mortality than patients from high-volume hospitals. CONCLUSIONS: Hospital volume of breast cancer surgical cases has a strong positive effect on 5-year survival. Research is needed to identify whether processes of care, especially postsurgical adjuvant treatments, contribute to survival differences.

Sarcomas of soft tissues after Vietnam service.

Vietnam service and military service experiences of 281 men with sarcomas of soft tissues were compared in this epidemiologic study to a control group of men derived from driver's license files and matched on 5-year period of birth and ZIP code of residence. No direct association was found for service in Vietnam (odds ratio, 0.53; confidence limits, 0.21-1.31) or for any military service (odds ratio, 0.53; confidence limits, 0.37-0.76). A multivariate matched logistic regression analysis showed similar results for Vietnam service while controlling for military service. Results also were similar when the 130 cases who had died were compared to a second control group derived from death certificates. Finally, no significant associations were found for "Agent Orange" or other variables that might be related to herbicide exposure.

Frequency, spacing, and outcome of pregnancies subsequent to primary cesarean childbirth.

A prospective study was conducted to determine the frequency, spacing, and outcome of pregnancies that occur subsequent to primary cesarean childbirth. A cohort of 5513 women, pregnant for the first time and with these pregnancies terminating with a live birth via cesarean childbirth, were followed for 5 years with use of the vital records registration system of the New York State Department of Health. Also followed was a group of women whose first pregnancy terminated with a live birth via vaginal delivery. The cesarean childbirth study group was found to have had 11% fewer pregnancies terminating during the follow-up period than did the vaginal delivery group. Subsequent live births among the cesarean delivery study group were, on the average, 1 week shorter in gestation and lower in birth weight than those of the vaginal delivery group. However, there was no excess of very low- or low-birth weight infants among the cesarean delivery study group. There was no difference between study groups in the spacing of subsequent pregnancies.

Cesarean sections in upstate New York, 1968-1978.

Data from birth certificates were used to examine the changing trends in the use of cesarean section from 1968 to 1978 in upstate New York. Differences in the percentages of primary cesarean section among population subgroups are cited. Hospital-to-hospital variation in the use of primary cesarean section is shown, as is the relationship among per cent primary cesarean section, hospital size, neonatal mortality, and the per cent of breech deliveries. The percentage of births delivered via cesarean section in 1978 is four times the percentage of 1968 (from 2.5-10.2% for whites, from 3.1-11.5% for nonwhites). Among the subgroups of the population, the increase has ranged from one and one-half to five times the 1968 percentage. There was little hospital-to-hospital variation in the percentage of primary cesarean section in 1968-1969; however, in 1977-1978 the per cent of deliveries performed by primary cesarean section varied from 1-22%. While neonatal mortality was found to be related to the percentage of cesarean section performed in hospitals in 1968-1969, no such association was found in 1977-1978. An inverse relationship was found between the percentage of breech deliveries and the percentage of cesarean sections performed in hospitals in 1977-1978.

Where people die.

Death certificates for 1977 filed with the New York State Department of Health were studied to determine where people died. Data were examined by the location and cause of death and by the age, sex, race, and marital status of the decedent. Comparisons were made with a similar study in which U.S. data were used for 1958 events. Approximately 60 percent of all the 1977 deaths in upstate New York occurred in hospitals; only 27 percent occurred outside an institution. The location of death varied by all the factors studied. Within all age categories, males had a higher percentage of hospital deaths. In those age categories in which nursing home deaths comprised a significant proportion of total deaths, females had a higher percentage of such deaths than males. Differences in the location of death according to its cause reflect the nature of the cause of death, for example, whether it was of sudden onset or the result of chronic disease. Most people do not consider in advance where they might die. The idea that age, sex, and marital status, as well as the more obvious cause, all play a part in the location may seem surprising. Yet all these factors were found to be associated withe location of deaths in upstate New York, and there is no reason to believe that this association does not hold true for the entire nation. More research, however, needs to be done based on more years and other geographic artal stutus may be instructive as to the present state of health resources.