Trends in childlessness in the United States, 1910–1975

Abstract

This paper examines trends in childlessness for ever‐married women in the United States. Data assembled from assorted census materials permit cohort and period investigations for a number of time periods, from 1910 to 1975, for various color and ethnic groups. Whether examined at the period or cohort level, the incidences in percentage rates of childlessness have varied irregularly over time. We focus particularly on the younger cohorts of white women (those beginning fecundity after 1965); they show higher rates of childlessness at each age than any of the older cohorts at similar ages in the reproductive cycle. We suggest that a major portion of the increasing rates of these younger cohorts may be attributed to increases in voluntary childlessness, which in turn may be linked to broader changes in the fabric of society regarding fertility control, contraceptive technology, female work preferences and patterns, and sexual and family norms.     

Household type and family size in Maharashtra, 1970

Abstract

Demographic transition theory expectations notwithstanding, empirical analyses have often observed higher fertility among nuclear than among extended households. A similar finding has been observed consistently at all stages of the reproductive career among a sample of households in Maharashtra, India, in 1970. Neither differential levels of natural fertility nor of family‐size preferences and use of fertility regulation, nor differential socioeconomic levels, can explain adequately the higher fertility of nuclear households. On the other hand, the evidence suggests that the direction of causation is reversed, that is, that household type is itself a function of fertility and other life‐cycle variables and also of space constraints on the household, and as such, is a better determinant of household type than a function of the latter.     

Growth rates of young-of-year shovelnose sturgeon in the Upper Missouri River

Information on growth during the larval and young‐of‐year life stages in natural river environments is generally lacking for most sturgeon species. In this study, methods for estimating ages and quantifying growth were developed for field‐sampled larval and young‐of‐year shovelnose sturgeon Scaphirhynchus platorynchus in the upper Missouri River. First, growth was assessed by partitioning samples of young‐of‐year shovelnose sturgeon into cohorts, and regressing weekly increases in cohort mean length on sampling date. This method quantified relative growth because ages of the cohorts were unknown. Cohort increases in mean length among sampling dates were positively related (P < 0.05, r² > 0.59 for all cohorts) to sampling date, and yielded growth rate estimates of 0.80–2.95 mm day⁻¹ (2003) and 0.44–2.28 mm day⁻¹ (2004). Highest growth rates occurred in the largest (and earliest spawned) cohorts. Second, a method was developed to estimate cohort hatch dates, thus age on date of sampling could be determined. This method included quantification of post‐hatch length increases as a function of water temperature (growth capacity; mm per thermal unit, mm TU⁻¹), and summation of mean daily water temperatures to achieve the required number of thermal units that corresponded to post‐hatch lengths of shovelnose sturgeon on sampling dates. For six of seven cohorts of shovelnose sturgeon analyzed, linear growth models (r² ≥ 0.65, P < 0.0001) or Gompertz growth models (r² ≥ 0.83, P < 0.0001) quantified length‐at‐age from hatch through 55 days post‐hatch (98–100 mm). Comparisons of length‐at‐age derived from the growth models indicated that length‐at‐age was greater for the earlier‐hatched cohorts than later‐hatched cohorts. Estimated hatch dates for different cohorts were corroborated based on the dates that newly‐hatched larval shovelnose sturgeon were sampled in the drift. These results provide the first quantification of growth dynamics for field‐sampled age‐0 shovelnose sturgeon in a natural river environment, and provide an accurate method for estimating age of wild‐caught individuals. Methods of age determination used in this study have applications to sturgeons in other regions, but require additional testing and validation.     

A regression approach to the projection of U.S. fertility based on past fertility data

Abstract

The method of fertility projection used by the U.S. Bureau of the Census involves assumptions about the ultimate cohort total fertility rate and the ultimate cohort mean age at childbearing based on recent levels of fertility and women's birth expectations. This paper provides an outline of a general regression approach to fertility projection based on past data which would generate these two ultimate cohort characteristics. The technique is illustrated by using the U.S. single‐year age‐specific fertility rates up to 1986 for total women and projecting them indefinitely into the future until they become stable for both calendar years and cohorts.     

Decline of tuberculosis mortality in an urban Mexican‐origin population, 1935–1984

Abstract

Through a series of life table analyses, this paper describes the natural history of tuberculosis mortality in a Mexican‐origin community over five decades (1935–84) during which the disease underwent a transition from a major underlying cause of death to a disease conditioned mentioned more often on death certificates as contributing to death than causing death. The decline in death rates from 1940 to 1950 was especially remarkable. Successive birth cohorts of Mexican Americans, separated by as little as five years of age, experienced distinctly lower risk of death from tuberculosis as they entered young adulthood. There was a rapid convergence in age‐specific patterns of tuberculosis death rates in Mexican Americans toward those of non‐Hispanic whites, so that by 1960 tuberculosis was primarily a cause of death in old age rather than young adulthood. The impact of changing environment, both through improvements of conditions within neighborhoods and through residential mobility, on birth cohorts at risk of tuberculosis needs to be examined in further research.     

A DEMOGRAPHIC TRANSITION ALTERED THE STRENGTH OF SELECTION FOR FITNESS AND AGE‐SPECIFIC SURVIVAL AND FERTILITY IN A 19TH CENTURY AMERICAN POPULATION

Modernization has increased longevity and decreased fertility in many human populations, but it is not well understood how or to what extent these demographic transitions have altered patterns of natural selection. I integrate individual‐based multivariate phenotypic selection approaches with evolutionary demographic methods to demonstrate how a demographic transition in 19th century female populations of Utah altered relationships between fitness and age‐specific survival and fertility. Coincident with this demographic transition, natural selection for fitness, as measured by the opportunity for selection, increased by 13% to 20% over 65 years. Proportional contributions of age‐specific survival to total selection (the complement to age‐specific fertility) diminished from approximately one third to one seventh following a marked increase in infant survival. Despite dramatic reductions in age‐specific fertility variance at all ages, the absolute magnitude of selection for fitness explained by age‐specific fertility increased by approximately 45%. I show that increases in the adaptive potential of fertility traits followed directly from decreased population growth rates. These results suggest that this demographic transition has increased the adaptive potential of the Utah population, intensified selection for reproductive traits, and de‐emphasized selection for survival‐related traits.     

Changes in Sibling configurations for American preschool children

Abstract

This paper uses data drawn from the 1940 through 1980 Public Use Microdata Samples of the U.S. Census of Population to document sibling configurations from the child's perspective. Changes in four aspects of siblings are examined for five cohorts of white and black preschool‐aged children: number, birth order distributions, spacing intervals, and sex composition. Changes in fertility behavior of adults in the post‐war era had a profound effect on the structure of sibling systems experienced by children. Successive cohorts of preschool children show a rise in number of siblings through the early post‐war years before showing sharp declines in number of siblings through the 1960's and 1970's. These shifts in size of sibling sets are reflected in changes in the proportion of each cohorts who are first born and only children, both of which have increased substantially by the 1980 cohort. The 1940 and 1980 cohorts have similar proportions of children with short intervals. However, the middle cohorts show the effects of the quickened pace of fertility with substantial proportions of children with comparatively short birth intervals. Finally, substantial shifts across cohorts in several measures of sex composition of children are observed. Most significantly, there is a marked decline in the proportion of children experiencing an opposite‐sex older sibling.     

An examination of factors influencing black fertility decline in the Mississippi Delta, 1880–1930

Abstract

Although the fertility decline in the black population in the Mississippi Delta between the late 1870's and early 1930's closely paralleled that of the national black population, it rose much more dramatically in the 1940's and 1950's to almost 1880 levels. Given the especially rural and oppressed conditions of blacks there, the initial decline seems puzzling. Low fertility rates in the 1930's reflected a large proportion of childless females. Investigations of changing contraceptive usage and mate exposure suggest both were minor components at most. Several physiological impairments were investigated including dietary deficiences, malaria, tuberculosis, and sexually transmitted diseases (STD). Evidence suggests STD played the major role, facilitated by nutritional and other health problems. Models relying heavily on those developed by McFalls and McFalls (1984) suggest 50–80 percent of the decline could have been due to the spread of STD. Age‐specific birth rates for different periods and post‐World‐War‐II fertility increases seem consistent with this finding.     

The estimation of natural fertility: A micro approach

Abstract

The estimation of natural fertility has heretofore been confined to population aggregates. This paper presents a technique for estimating natural fertility at the household level for developing countries with some practice of deliberate family size limitation and applies it to micro‐level WFS data for Sri Lanka and Colombia for females aged 35–44 in intact marriages. The technique is based on a proximate determinants equation estimated as part of a model that takes account of the interdependence between use of fertility control and natural fertility. To evaluate the results, the mean and household level estimates of natural fertility for each country are first compared with actual fertility; then mean estimates for each country are compared with macro‐level estimates of natural fertility based on three other methods. Finally, the implications of the analysis for the proximate sources of intercountry and intracountry variations in natural fertility are examined. The results suggest that the present approach yields plausible quantitative estimates of natural fertility and reasonable analytical results.     

The pattern of reproductive life in a Berber population of morocco

Abstract

Reproductive patterns were studied from data collected in 1,450 Berber households in the province of Marrakesh, Morocco in 1984. Women aged 45–49 years had a mean of 8.9 pregnancies to achieve 5.7 living children. Social influences on fertility rates show the importance of tradition, particularly through time‐dependent variables such as age at marriage, waiting time to first birth, interbirth intervals, and duration of breastfeeding. Birth control does not appear to affect the tempo of fertility; rather, its main use is to bring the reproductive period to a close. The comparison of two subsamples of women separated by a 25‐year interval indicates an actual acceleration of the tempo of fertility by the reduction of waiting time to first birth and of interbirth intervals. The supposed ongoing process of demographic transition is not clearly observed in this population.     

Adoption of fertility limitation in an American frontier population: An analysis and simulation of socio‐religious subgroups

Abstract

This paper investigates a late nineteenth‐century fertility transition in a predominantly Mormon population of the western United States. A unique set of longitudinal data composed of 31,500 computerized family genealogies is drawn upon to examine a number of problems identified in reappraisals of fertility transition research (Caldwell, 1981; Freedman, 1979). Four subcohorts, differentiated by religious commitment and exposure to urban influences, are examined over the course of the transition. The study presents traditional analyses of subcohort CEB levels, period MTFR's, and m values (Coale and Trussell, 1974) and focuses on a macrosimulation of the fertility transition within the population (Bongaarts, 1976). Despite wide subcohort variation in cross‐sectional levels of fertility over time, simulation results suggest a similar absolute longitudinal decline in fertility levels, parity at which contraception was initiated, and maximum birth parities for all four subcohorts. The implications of these results for future analyses and the desirability of individual level data are discussed.     

Farm background,socioeconomic status,and fertility: The two‐generation hypothesis

Abstract

This paper reports on an examination of 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 two‐generation‐urbanite hypothesis first advanced by Goldberg. Unlike a number of other studies, the findings do not support the hypothesis. Reasons for the lack of support are discussed, and methodological weaknesses of previous studies are identified.     

The disadvantaged child: A product of the culture of poverty,his education,and his life chances

Abstract

This study concerns the fertility of Sherpa and Tibetan women living at altitudes over 3,400 meters in Nepal. The average completed fertility (4.77 live births) and estimated crude birth rate (31 to 33 per 1,000) are low relative to low altitude peasant populations as well as to high altitude Andean peasants. Environmental phenomena (hypoxia, iodine deficiency) may be associated with retarded menarchial age and high infant mortality; but the major factors causing the low fertility appear to be cultural rather than environmental. Traditional ceremonial requirements delay the age at marriage until the mid or late twenties. Religious practices promote male and female celibacy. Migrant females and women married to migrant males report reduced fertility, probably because of poor nutrition and health care. Nonmigrant women living in villages that participate extensively in the cash economy have greater access to the growing market economy, health care, and education and report higher numbers of live births and fewer child deaths.     

Changes in contraceptive use and fertility: Panama, 1976 to 1984

Abstract

From 1976 to 1984 important demographic changes occurred in Panama. The total fertility rate declined from 4.5 to 3.7, and contraceptive use amongmarried women 20–44 years of age increased from 55 per cent to 63 per cent. However, using data from three national level reproductive health surveys which were conducted in Panama in 1976, 1979, and 1984, we found that most of the changes took place between 1976 and 1979. Since 1979, overall contraceptive use and fertility have remained virtually unchanged, although there has been an important method‐mix shift toward an increase in the use of contraceptive sterilization and IUD's, with an accompanying decline in the use of oral contraceptives. Although the singulate mean age at marriage remained relatively constant, the average duration of breastfeeding rose 23 per cent during the period. Further gains in contraceptive prevalence and reduction in unplanned fertility in Panama will largely depend on enhanced program efforts first begun in the early 1970's by the Panama Ministry of Health. Future program efforts especially should be directed toward encouraging young couples to space their children more effectively by using temporary methods of contraception.     

IUCD acceptors in Trivandrum,Kerala, South India

Abstract

Previous tests of the economic theory of fertility using multivariate regression techniques have generally analyzed only cross‐sectional data. Some students of fertility, notably Janowitz (1973a,b), have argued that such studies must also be conducted with change data. This paper presents tests of the economic theory of fertility with both cross‐sectional and change data for the 48 contiguous states. The cross‐sectional analyses examined the effects of male and female income on the marital fertility of 20–24 year olds for 1950, 1960, and 1970 while controlling for the effects of education, urbanization, race, religion, and population density. Controlling for the effects of the same noneconomic variables, a second set of multivariate regression analyses examined the effects of changes in male and female income on changes in the level of marital fertility of 20–24 year olds during the 1950–60 and 1960–70 periods. Both the analyses with cross‐sectional data and change scores provided support for the economic theory.     

Period and cohort dynamics in fertility norms at the onset of the demographic transition in Kenya 1978-1998

A characteristic of African pre-transitional fertility regimes is large ideal family size. This has been used to support claims of cultural entrenchment of high fertility. Yet in Kenya fertility rates have fallen. In this paper this fall is explored in relation to trends in fertility norms and attitudes using four sequential cross-sectional surveys spanning the fertility transition in Kenya (1978, 1984, 1989 and 1998). The most rapid fall in the reported ideal family size occurred between 1984 and 1989, whilst the most rapid fall in the total fertility rate occurred 5 to 10 years later, between 1989 and 1998. Thus these data, spanning the fertility transition in Kenya, support the traditional demographic model that demand for fertility limitation drives fertility decline. These data also suggest that the decline in fertility norms over time was partly a period effect, as the reported ideal family size was seen to fall simultaneously in all age cohorts, and partly a cohort effect, as older age cohorts reporting higher ideal family sizes were replaced by younger cohorts reporting lower ideal family sizes. These data also suggest that a new fertility norm of four children may have developed by 1989 and continued until 1998. This is consistent with, and perhaps could have been used to predict, the stall in the Kenyan fertility decline after 1998.     

A population-based age-period-cohort study of colorectal cancer incidence comparing Asia against the West

BackgroundColorectal cancer (CRC) is the third most common cancer worldwide but incidence varied widely. Despite the role of genetics, CRC is also sensitive to macro-environmental factors. Few studies have ever compared across different countries/regions to suggest possible macro-environmental risk factors of CRC. We estimated the effects of age, period and cohort on the changes of incidence of colorectal cancer across different countries/regions.MethodsPoisson regression age-period-cohort (APC) models were conducted to estimate the age, period and cohorts effects on CRC incidence across the West (i.e., the UK, the US and Australia) and Asia (i.e. Japan, Hong Kong, Shanghai, Singapore and India). We maximized the length of the study period according to each country’s data availability.ResultsWestern populations show upward inflections for their 1950s–1960s cohorts, while Asian populations (except India) show downward inflections for their 1950s cohorts. Japanese population also shows upward inflections for its 1960s cohorts, similar to the Western populations. There are apparent upward inflections towards the more recent cohorts for Hong Kong, Shanghai and Singapore; nevertheless, the confidence intervals are wider towards the more recent cohorts.ConclusionOur findings imply an increasing risk of CRC in both Western and Asian populations as their younger cohorts reach older ages. These findings are consistent with the life course argument that macro-environmental changes associated with socio-economic development have specific effects that extend over the life course. Actions that pertain to altering lifestyle-related exposures over the life course are of great importance in combating young CRC risks in the future.     

Renal bioaccumulation of trace elements in urban and rural Sri Lankan populations: A preliminary study based on post mortem tissue analysis

IntroductionEnvironmental pollution, especially by toxic trace elements, is a global health concern. Heavy metals such as Cadmium (Cd), Arsenic (As) and Lead (Pb) are associated with numerous disorders and are considered by some as an aetiological factor for the Chronic Kidney Disease (CKDu¹) epidemic in Sri Lanka. This study explores patterns of bioaccumulation of six trace elements in kidneys obtained during forensic autopsies from urban and rural regions in Sri Lanka.MethodsKidney samples obtained from one urban district (n = 13) and three rural districts (n = 18) were lyophilized, microwave digested and profiled by ICP-MS techniques.Results and DiscussionThe mean age of the sampled population was 47.9 ± 11.3 yrs. Median (IQR) for Cd, As, Pb, Cr, Zn and Se were, 14.67(8.04–22.47) μg/g, 0.44(0.29–0.56) μg/g, 0.11(0.07–0.30) μg/g, 0.15(0.1096–0.3274), 25.55(17.24–39.35) μg/g and 0.52(0.37−0.84) μg/g, respectively. Cd, Zn and Se levels were significantly higher (p < 0.05) among the urban samples compared to that of the rural group. Zn and Se levels were higher among younger age groups. As, Pb and Cr did not show any significant differences between the two cohorts nor any correlations with age.ConclusionThis population-specific baseline study provides an insight into the differences in exposure to toxic trace elements and essential elements between urban and rural populations. Residents in CKDu affected rural districts did not appear to be at risk of toxic heavy metal exposure, however their renal bioaccumulation of nephroprotective essential elements was lower than urban residents.     

Changes in growth and maturation parameters of Pacific sardine Sardinops sagax collected off California during a period of stock recovery from 1994 to 2010

Whether fluctuation in density influenced the growth and maturation variables of three aggregated cohorts (fish born during the 1986–1993, 1996–2003 and 2004–2008 periods) of Pacific sardine Sardinops sagax caeruleus collected off the Californian coast from 2004 to 2010 was investigated. Using a von Bertalanffy mixed‐effects model with aggregated cohorts as covariates, estimated growth rate significantly covaried with aggregated cohorts. Growth rate (K) was modelled as a fixed effect and estimated to be 0·264 ± 0·015 (±s.e ). Statistical contrasts among aggregated cohorts showed that the 1996–2003 cohorts had a significantly lower growth rate than the other two aggregated cohorts. The theoretical age at length zero (t₀) and the standard length at infinity (L_S∞) were modelled as random effects, and were estimated to be ?2·885 ± 0·259 (±s.e ) and 273·13 ± 6·533 mm (±s.e ). The relation of ovary‐free mass at length was significantly different among the three aggregated cohorts, with the allometric coefficient estimated to be 2·850 ± 0·013 (±s.e ) for the S. sagax population. The age‐at‐length trajectory of S. sagax born between 1986 and 2008 showed strong density dependence effects on somatic growth rates. In contrast to the density‐dependent nature of growth, the probability to be mature at‐size or at‐age was not significantly affected by aggregated cohort density. The size and the age‐at‐50% maturity were estimated to be 150·92 mm and 0·56 years, respectively. Stock migration, natural fluctuations in biomass and removal of older and larger S. sagax by fishing might have been interplaying factors controlling growth parameters during 1986–2010.