Desired family size, family planning and fertility in Ethiopia

This paper models the proximate determinants of children born to over 13,000 Ethiopian women and of the women's stated preferences for additional births using the data from the Ethiopian Demographic and Health Survey 2000. Empirical models for the number of children born to women were estimated using Poisson and ordinal regressions. The results show the importance of variables such as maternal education for smaller family size, and that variables reflecting desired family size are strong predictors of the numbers of children born to women. Secondly, binary logistic models for dichotomous variables for women not wanting more children and if getting pregnant would be a 'big problem' showed non-linear effects of the surviving and 'ideal' number of children. Moreover, the results indicated a desire on the part of women to limit family size, especially as the number of surviving children increased. Probit models were estimated to address potential endogeneity of certain variables. Overall, the results indicated that counselling couples about small family size and increasing the utilization of health care services can lower fertility in Ethiopia.     

Sex of children and family size: a decision model

Parents often manifest the desire to have children of both sexes, and this wish sometimes influences their actual reproductive behavior. If sibship size were selectively limited once the above objective was achieved, would the sex sequences of completed families still present a random character? In order to answer that question, a decision model reproducing the enlargement strategy of families relative to sex criteria was created. By simulation, it was shown that family limitation based on sex composition entails a positive association between sexes of consecutive children in fictitious families. Such a property has indeed been detected in some samples of real families, thus supporting the present model. However, it may also be attributed to biological factors.     

Sex of children and ultimate family size by time and class

Abstract

Data from this study and five earlier studies are analyzed to determine the magnitude and significance of the influence of sex combinations of prior children upon the ultimate (or completed) number of children in the family. In addition to confirming the observation of earlier investigators that the influence of combinations of sexes in the first two children differs by geographic area, it is shown that a difference has occurred in a single region over time, and the data for the most recent cohort suggest an effect of social class as well. Three measures of association (the corrected odds ratio, the natural logarithm of this ratio, and the fourfold point correlation) point to a small magnitude of the influence studied even when it is present at a statistically significant level. Notes on sample size relative to levels of α and β errors are included, as is discussion of a valid method of combining contingency tables.     

Human sex ratios and sex distribution in sibships of size 2

We previously analyzed data from the U.S. National Health Interview Survey (NHIS, 1998 to 2002) on families with two biological children (10 years of age and younger) and found that the distribution of families with two boys, two girls, and one boy + one girl did not statistically conform to a binomial distribution regardless of the boy/girl sex ratio used. Using the best estimate of the sex ratio from the data, we found that there were significantly more families with opposite-sex siblings than families with same-sex siblings. No biological mechanism could explain these results at the time. In the present study we conducted an analysis of the first two children in sibships of size 3 from the same data source and found that there are significantly more same-sex sibships than unlike-sex sibships. Combining the two sets of data for the first two children produced observed numbers in close agreement with the expected numbers. A hypothesis of parental choice (family planning) appears to be strongly supported as an explanation for the discrepancies in the two sets of data individually. For example, parents who have a boy and a girl (either order) as their first two children are more likely to stop having children ("stopping rule") than are parents whose first two children are of the same sex.     

Family configuration and family size

Abstract

In a sample of 61,829 families, the probability of having an additional child is higher in those families with all children of the same sex as compared to those families with children of both sexes. In addition, families with only boys were more likely to have an additional child than families with all girls.     

Family configuration and family size

In a sample of 61,829 US families, the probability of having an additional child is higher in those families with all the children the same sex as compared to those families with children of both sexes. Data are from families of American high school students who took the National Merit Scholarship Qualifying test in 1965. All families with 3 or 4 children were selected. Families with only boys were more likely to have an additional child than families with all girls. Less than 1% of the variance in family size is explained by family configuration. Although the sample size makes these results unequivocal for the population involved, the population is clearly biased in favor of white middle class families.     

Nest size and hatchling sex ratio in chinstrap penguins

Variation in the sex ratio at hatching in the chinstrap penguin Pygoscelis antarctica was investigated, using molecular sexing to test predictions of sex allocation theory. The sex ratio was slightly male-biased (0.54) but did not differ significantly from parity. The proportion of males increased with nest size, an estimator of parental quality in chinstrap penguins. High-quality parents were able to produce and rear a higher proportion of male offspring, the more costly sex in this slightly sexually dimorphic species. Our results may be in agreement with Trivers and Willards (1973) argument on biases in the offspring sex ratio being contingent on parental condition or quality.     

Measures of family size preferences

This study is based on questionnare data from cohorts of women in England and Wales married once only in the 1950s and 1960s. It uses estimates of preferred family sizes derived from those achieved at various durations of marriage, using a Monte Carlo simulation model of reproductive histories, slightly modified in its representation of breastfeeding. The method of estimation consists in inverting the relationship between these 2 distributions (wanted and achieved births) which form respectively an input to and an output of the model. The model is explained in detail. The increasing preference for families of 2 children is shown in cohorts married in 1951, 1956, 1961, 1966, and 1971 for women's ages at marriage 20-24 and 25-29. The trend is paralleled in the findings of World Fertility Surveys of 11 countries plus the US. Sensitivity to assumptions regarding contraceptive effectiveness is tested, and ranges established for estimates. The 2-child trend is discussed in light of theories relating individual and societal consciousness that 2 children are optimum from the points of view of family and societal welfare. On the family level the 2-child family has implications even over generations, with regard to family support needed for very young or old populations.     

The relation between small size for gestational age and the sex ratio of children with birth defects

BACKGROUND: Infants with birth defects are more likely to be born small for gestational age (SGA) than are other infants. This study describes a relation noted between the percentage SGA and the percentage male among children with various defect types. The data source was case records collected by the Metropolitan Atlanta Congenital Defects Program, a population-based, active surveillance system, during 1968 through 1998. METHODS: The study calculated the correlation between the percentage male and the percentage SGA for isolated cases of 44 different defect types for male-dominant and female-dominant defects separately. RESULTS: The correlation coefficient was -0.47 (P < 0.01) for male-dominant defects and 0.20 (P > 0.05) for female-dominant defects. Male-dominant defects were more likely to show less than 15% SGA and more likely to show the strongest risk differences by sex. CONCLUSIONS: These results are consistent with genetic causation of strongly skewed sex ratios, at least among male-dominant defects. Review of the literature suggests that defects with sex ratios closer to 1 are likely to have lower recurrence risks and therefore are less likely to be inherited than are other defects with skewed sex ratios. Sex ratios closer to 1 and a high percentage SGA may be markers of acquired or environmental birth defects.