Life expectancy of monozygotic and dizygotic twins.

White male twins from the NAS-NRC twin sample, who were born in the U.S. between 1917 and 1927 and served in the military, are used to estimate variability in hazard functions for those twins who died during the period 1974-1990. Roughly the same number of MZ and DZ twins died during this period, but their death rates are similar. DZ twins exhibit greater within-pair variation. Using hazard and other analyses, the only statistically significant variables are found to be being a DZ twin (in level equations), date of birth, and, sometimes, wife's religious preference. Variables not significant for level or within-pair equations, include own religion, parental education, working overtime frequently, and number of children. The greater variation in life expectancy of DZ twins is hardly surprising and may say something about the lack of comparability in phenotype variance of DZ twins, which in turn may be worrying.

Age-specific death rates with tobacco smoking and occupational activity: sensitivity to sample length, functional form, and unobserved frailty.

In this article, we estimate accelerated time-to-failure and proportional-hazard functions with about 100,000 members of the Dorn sample, finding greater hazards associated with smoking and some dependence on occupational variables that measure risk and physical activity. We answer three questions: (1) How sensitive are the estimates to sample length, using monthly data for the periods 1954-1969 and 1954-1980? The results differ somewhat between these sample periods. (2) How sensitive are the estimates to alternative functions for the hazard? Within a given time period, the estimates are fairly robust to specification changes in the distribution of the hazard in the accelerated time-to-failure models. (3) How sensitive are the estimates to alternative controls for unobserved frailty? Within a given sample period, the estimates are fairly robust to the allowance for parametric or nonparametric heterogeneity in the proportional-hazard models.

A comparison and latent variable test of two fertile ideas.

A test is constructed to distinguish between the Becker and the Easterlin models of the economics of fertility. Both suggest possible biases due to unobserved variables. It is demonstrated that "while the Becker endowment and Easterlin taste models can be expressed in terms of the same variables, it is possible to identify each of the models because of different signs in a latent variable system that uses information from individuals, siblings, and cousins. Estimates of this model are consistent with the Easterlin, but not the Becker formulation. But neither model results in significant income coefficient estimates." The geographical focus is on the United States.

A test of the Easterlin fertility model using income for two generations and a comparison with the Becker model.

An important dimension of Easterlin's seminal work on fertility is the hypothesis of intergenerational taste formation, or the relative income hypothesis. Previous estimates have not had data on income in two generations, so the estimated own-income effects may have had a downward bias. This article uses data with income from two generations to estimate the Easterlin model directly. Own income is still not positively significant. A simple single-equation test is developed to distinguish this model from a Becker intergenerational serially correlated endowments model that he claims is observationally equivalent. The test results favor the Becker formulation.

Birth order, schooling, and earnings.

"Birth-order effects are posited by many to affect earnings and schooling. We show how such effects can be interpreted to shift either the earnings possibility frontier for siblings or parental preferences. We find empirical evidence for birth-order effects on (age-adjusted) schooling and on earnings for young U.S. adults, though the latter is not robust for all specifications. The examination of intrahousehold allocations suggests that these birth-order differences occur despite parental preferences or prices by birth order favoring later borns, apparently because of stronger endowment effects that favor first borns."

Effect of number and position of siblings on child and adult outcomes.

PIP: This paper develops a theoretical model of the effects of family size and birth order on educational attainment and earnings. The parental utility maximization model allows the development of closed-form expressions for the within-family ratios of schooling and earnings. A reduced form demand function for each child's schooling and earnings also can be obtained. Each of these functions depends on the exogenous variables of the price of education divided by the price of parental consumption, parental income, the child's endowment, and the parameters of the utility and the production function. Application of this model to empirical data from the Twin and Adult Offspring Sample confirmed both birth order and family size effects for schooling even when parental age, income, education, and father's religion were controlled. The effects were larger for daughters than sons. The difference in educational attainment between 1st and 5th-born was 0.7 years for males and 1.4 years for females. Family size further reduces parental contribution to college education and encourages working, loans, and scholarships. The earnings data do not display birth order effects once family background and sibship size are controlled.^ieng

Earnings, education, genetics, and environment.

A major and well-recognized difficulty in estimating the effects of education on earnings is that the more educated are likely to be more able, irrespective of education. If ability also determines earnings and is not controlled, ordinary least squares will yield biased estimates of the education coefficient. In this study, we use data on identical twins to control for differences in ability that arise from genetic endowments and family environment. Not controlling for genetics and family environment may cause a large bias, up to two-thirds of the noncontrolled coefficient.