Menarcheal age and subsequent patterns of family formation.

We examine whether age at menarche affects age at first marriage or first birth using two samples of U.S. women. Data are drawn from the Tremin Trust, a longitudinal study of menstrual cycles that recruited white women who were students at the University of Minnesota and from a survey of a nationally representative sample of white women born between 1900 and 1910. Regression models with cubic splines were used to analyze the relationship between age at menarche and age at first marriage. Cox proportional hazard models were used to examine the effect of age at menarche on the interval between marriage and first birth. Unlike earlier work, we found that once secular trends in both age at marriage and age at menarche were taken into account, there was no evidence that age at menarche affects either age at marriage or the timing of first births in these U.S. women.

High fertility of Old Colony Mennonites in Mexico.

Old Colony Mennonites in Mexico appear to demonstrate natural fertility, using no form of artificial birth control and apparently not attempting to limit family size. The resulting fertility is nearly as high as that of the Hutterites, although the Mennonites lack the communal economic system of the latter. Most Mennonites in Mexico migrated from Canada in the 1920s, and the largest single settlement, called the Manitoba Colony, is one of four in the state of Chihuahua. A 1967 partial census obtained data from 38% of the Mennonite households. Family size in the sample was close to that in a local survey taken in the same year. Available church records matched with census forms permitted verification of and corrections to 560 female reproductive histories. The median number of live births to women over age 45 years was 9.5, compared with 10.4 in the Hutterites. Age-specific marital fertility rates and birth intervals closely resembled those of the Hutterites.

PIP: Old Colony Mennonites in Mexico appear to demonstrate natural fertility, use no form of artificial birth control, and are apparently not attempting to limit family size. The resulting fertility is nearly as high as that of the Hutterites, although the Mennonites lack the communal economic system of the latter group. Most Mennonites in Mexico migrated from Canada in the 1920s and the largest single settlement, called the Manitoba Colony, is 1 of 4 in the state of Chihuahua. A partial census in 1967 obtained data from 38% of the Mennonite households. Family size in the sample was close to that of a local survey taken in the same year. Available church records matched with census forms permitted verification of and corrections to 560 female reproductive histories. The median number of livebirths to women over age 45 was 9.5 compared with 10.4 in the Hutterite community. Age- specific marital fertility rates and birth intervals closely resembled those of the Hutterites.

Farm background, socioeconomic status, and fertility: the two-generation hypothesis.

PIP: This paper examines whether the effects of farm background on socioeconomic differentials in fertility are diminished among nonfarm couples. The data are for a sample of white ever-married women belonging to the 1901-1910 birth cohorts. The research provides another test of the 2 generation-urbanite hypothesis 1st advanced by the Goldberg studies of Detroit and Indianapolis. Unlike a number of other studies, the findings do not support the hypothesis. Thus, a number of questions arise concerning the results obtained by previous investigators in support of this hypothesis. Different types of samples measuring farm background and socioeconomic status may be plausible explanations for the differing results. It is also important to note that both the Detroit and Indianapolis samples can hardly be considered representative of US urban populations in the 1940s and 1950s. A further difficulty with the Detroit study was that Goldberg aggregated the data of a relatively large number of cohorts. The Indianapolis sample was constrained by the eligibility requirements of the original study. The difficulties of adequately testing Goldberg's hypothesis may have been compounded by the extension of the hypothesis to nationally representative samples. Moreover, The hypothesis was not supported when education was used as a measure of socioeconomic status in the Detroit study. Until other studies can be carefully replicated, definitive answers to such questions as to whether fertility differentials by socioeconomic status will disappear or have become attenuated must remain an unanswered question.^ieng

Fertility control in the United States before the contraceptive revolution.

PIP: Women born in the 1st decade of the 10th century achieved the lowest average family size of any cohort of US women that has completed childbearing. A survey of white, ever married women whose childbearing years peaked during the 1920s and 30s whows that more than 70% practiced contraception, and that over 80% of contraceptors used the most modern methods then available. Although few admitted to use of sterilization for contraceptive purposes, nearly 30% were surgically sterilized before age 50, and the pattern suggests considerable use for contraceptive reasons. Those born in the latter 1/2 of the decade, who reached their peak reproductive years during the Depression, were more likely to have practiced contraception and to have used a modern method than those born earlier. Women who had 2 or more live births, those who were college educated, urban, white collar and non-Catholic were also more likely than others to have used contraception. There was considerable use of contraception to space children as well as to terminate childbearing. Only 3% reported having had an induced abortion, but the data suggest that many reported induced abortions (then mostly illegal) as miscarriages and stillbirths.^ieng

Recall and reliability of interview data from older women.

Retrospective fertility histories were collected from a purposive sample of 211 white, ever-married women, residing in four metropolitan areas of the USA and belonging to the birth cohorts of 1901-1910. At the time of interview, these women were aged 66 to 76. A random sample of 50 of the original respondents was reinterviewed by telephone on selected topics from the questionnaire. Responses to questions on dates and numbers of marriages, as well as births and other fertility events were coded to show whether the responses were exact, estimated by the respondent, or calculated by the editors. Respondents provided exact answers to an average of 90% of the questions they were asked. Reliability ratios, which were calculated for the above variables as well as ever-use of contraceptive methods, were comparable with those observed in previous studies of women in the childbearing years.

Truncation effect in closed and open birth interval data.

PIP: A numerical investigation using a flexible simulation model to establish interval analysis as an index for changing natality patterns. Such an index should reflect parity distribution, the age at which women start reproduction, and the spacing of their births. The simulated statistical results illustrate the truncation effect that reflects a negative correlation between parity and the length of closed and open intervals in a birth or marriage cohort. Truncation is related to the duration of marriage at survey, but this duration interacts with other assumptions. Holding duration constant does not ensure that the data on intervals will reflect postulated changes in the distributions. For complete birth orders, this analysis does reflect patterns of child spacing. However, it ignores changes in the parity distribution, whether produced by deliberate limitation of family size or by the onset of secondary sterility. This difficulty is not overcome by life table analysis except under highly restrictive assumptions. It is doubtful whether the current emphasis on securing such data is justified. Further investigation is needed to provide a better basis for the definition and analysis of interval data if they are to be used.^ieng

An analytic simulation model of human reproduction with demographic and biological components.

Abstract This Monte Carlo model for simulating the reproductive history of a cohort of women is described in detail. The model provides for patterns of survival, sterility, formation and dissolution of sexual unions, fecundability, lactation, foetal wastage, family planning practices etc. Natality indices specific for marital status, for duration of marriage and for age, as well as analyses of birth spacing patterns are among the results that may be obtained. In the model, the experimental unit is an individual woman. The complete life history of a woman is generated and recorded before the history of the next woman is generated. The data for the whole cohort are analyzed at the end of the programme. The model includes two kinds of states into which a woman may pass, namely: (1) permanent changes of status such as death, sterility, or becoming a family planner, and (2) temporary states, each with a probability distribution of length of stay. The probabilities of the various events or changes of state may vary from age, parity, and other features of a woman's status or history. Natural fecundability at any age may also vary from woman to woman. In this programme natality patterns and specific indices such as age-specific fertility rates are produced, in a quasi-realistic fashion, by the interplay of the demographic and biological parameters postulated for any cohort. Consequently, the effect of changes in anyone factor can be studied, as well as the interaction resulting from changes in several factors. The purposes and potentials of the model are both substantive and methodological. As an illustration, a series of computer runs attempting to simulate the reproductive patterns of Indian women is presented. These results, as well as some additional ones, indicate some effects of changes in marital patterns, levels of fecundability, duration of post-partum non-susceptibility, age incidence of sterility and foetal wastage. In the final section of the paper, the advantages and possible applications of the model are discussed together with the limitations encountered to date in the efforts to apply the model.