In an effort to assess the relative importance of age at first birth, age at subsequent births, and total parity to the occurrence of breast cancer, reproductive data from 4,225 women with breast cancer and 12,307 hospitalized women without breast cancer were analyzed by a multiple logistic regression model. Age at first birth was confirmed to be the most important reproductive risk indicator; it was associated with a 3.5% increase of relative risk for every year of increase in age at first birth (the 95% confidence interval of this estimate was 2.3 to 4.7% increase per year). However, age at any birth after the first was also an independent and statistically significant risk indicator; it was associated with a 0.9% increase of relative risk for every year of increase in age at any (and every) birth (the 95% confidence interval of this estimate was 0.4 to 1.5% increase per year). There is evidence that the age of approximately 35 years represents for every birth a critical point; before this age any full-term pregnancy confers some degree of protection; after this age any full-term pregnancy appears to be associated with increase in breast cancer risk. The effect of parity is determined by the age of occurrence of the component pregnancies. While most pregnancies occur under the age of 35, the distribution varies from population to population, and this may account for the differences between populations in whether or not a protective effect is seen for births after the first, and if it is seen, its extent.

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Data from a large international case-control study of breast cancer suggested that women born to young mothers had a 25% lower risk of breast cancer. The association was not secondary to a tendency for these women themselves to have had children at early ages. The data provided no indication of a meaningful association between breast cancer risk and birth rank. Confounding was controlled by stratification according to a summary confounder score.

A study of smoking habits among high school students as related to smoking habits of their parents, and fathers' occupations revealed an increasing proportion of smokers with decreasing social class. Other aspects were studied and the authors discuss their findings with respect to other studies and future research.

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The purpose of this study is to re-examine the concepts of health services utilization presented by White and his colleagues in 'The Ecology of Medical Care'. We re-test their model in a rural population in the southern United States using longitudinal instead of cross-sectional data and find that the general principles of the 'Ecology' model do, indeed, apply to rural populations like Rougemont/Bahama. Use of this model has implications for modifying and improving the organization of the health care delivery system and for a fundamental change of emphasis in medical education.