Voluntary sterilisation among Canadian women

Using data from the 1984 Canadian Fertility Survey, proportional hazards modelling was employed to determine factors associated with the likelihood of voluntary sterilisation among 5315 women of childbearing age, and the trends in timing and differences in the likelihood associated with different age cohorts. Multivariate analysis suggests that educational attainment, parity and duration since last birth at the time of sterilisation, religious commitment, province of residence and marital status at the time of sterilisation, are all important predictors. Education and parity attainment emerged as the best predictors of the timing of voluntary sterilisation in all age cohorts, but the contribution of other covariates varies between cohorts.     

Covariates of age at first birth in Guyana: a hazards model analysis

Analysis of data from the Guyana Fertility Survey on the trends and covariates of age at 1st birth among various birth cohorts of women ever in union indicates that an early entry into union is associated with young age at 1st birth and higher number of children born. Multivariate analysis showed that women with higher education, urban residence, and entry into 1st birth compared to others, and that young women are delaying their 1st birth for longer durations than older women. Work status of women before 1st birth and the starting age of union seem to be the 2 major contributory factors for age at 1st birth. Noticeably, the role of education has changed and is now more significant among younger cohorts than among older ones for 1st birth timing.     

Changes in the timing of births in Melbourne, Australia

2 10-year marriage cohorts from 2 surveys of married women in Melbourne were compared on their timing of the 1st and 2nd births. The results showed that women who were married in the early 1970s were much more likely to delay their first birth until about the 3rd or 4th year of marriage compared with women who married in the 1960s. This tendency to delay the 1st birth was probably aided by effective contraception, as it coincided with widespread use of the oral contraceptive. There was no difference in the timing of the 2nd birth in relation th the 1st birth between the 2 marriage cohorts. Women who delayed childbearing also preferred smaller families. Indeed, the increase in the % of women delaying childbearing appears to be synonymous with the trend toward the two-child family. Altough the number of married women in the labor force increased significantly from the early to the later cohort, a desire to work was not usually cited as the reason for delaying childbearing. Rather, economic reasons were most frequently mentioned for delaying childbearing.     

Education and timing of parenthood among Canadian women: a cohort analysis.

This research examines factors associated with the timing of first birth in Canada, focusing primarily on the role of women's educational attainment. Proportional hazards modelling techniques are applied to data from the 1984 Canadian Fertility Survey (CFS) in order to determine how educational attainment, estimated as close as possible to the date of first birth, influences the timing of first birth and whether the importance of this variable varies according to age cohorts. The results suggest that among a number of variables useful for distinguishing different levels of risk, educational attainment proves to be the most important predictor in the model. Education exerts a substantial positive influence on birth timing for women of all age groups. As expected, moreover, significant cohort differences are also evident, with the greatest to the smallest impact on the risk from the youngest to the oldest cohorts. These clear-cut cohort differences indicate a fundamental change in the effects of education over time, a trend most likely resulting from substantial changes in both the content and social significance of formal schooling during the past few decades.     

Alternative theories of the relationship of schooling and work to family formation: evidence from Mexico

Role incompatibility, education as an investment in human capital, and schooling as a transformative experience are three mechanisms that link women's education to the timing of marriage and first birth. We simultaneously evaluate these different explanations using retrospective life history data for two cohorts of Mexican women collected in a nationally representative sample. Our analyses provide evidence in support of all three hypotheses. While in school young women are at a substantially lower risk of marriage and of a first birth. We find no evidence that women leave school to enter into unions nor do we find evidence that the effect of being a student diminishes with age. Women who work for a wage are also at a lower risk of marriage and a first birth. Once we control for student and employment status, the direct effects of cumulative education on family formation are relatively modest, although cumulative education is strongly associated with positive attitudes towards women's work and a significant increase in the likelihood of premarital and postmarital employment.     

Effects of seed release timing on plant life-history and seed production in a population of a desert annual,shape Blepharis sindica (Acanthaceae)

Growth, phenology, survivorship, and seed production were observed in a population of a desert annual, Blepharis sindica, with reference to the variation in the timing of seedling emergence. The population consisted of several cohorts induced by rain-cued seed release within a growing season. The fate of 100 individuals of six cohorts was monitored throughout the growing season. Earlier-established cohorts had significantly larger plant sizes and higher reproductive outputs than later cohorts. The time and duration of each phenological stage varied among the cohorts, and they were also influenced by plant size. Mortalities at the seedling stage, vegetative stage, and reproductive stage increased with the delay of seed release. Seed release was concentrated in the early growing season. Fecundity was highest in the earliest cohort and decreased monotonically in later cohorts. The results suggested that even in temporally varying environments, the superiority of early emergent plants was evident. The seed release patterns in temporally fluctuating desert environments are discussed as a compromise between 'diversified bet-hedging' and an optimal timing for maximizing the reproductive success in a growing season.     

Simulated natural day lengths synchronize seasonal rhythms of asynchronously born male Siberian hamsters

Photoperiodism research has relied on static day lengths and abrupt transitions between long and short days to characterize the signals that drive seasonal rhythms. To identify ecologically relevant critical day lengths and to test the extent to which naturally changing day lengths synchronize important developmental events, we monitored nine cohorts of male Siberian hamsters (Phodopus sungorus) born every 2 wk from 4 wk before to 12 wk after the summer solstice in a simulated natural photoperiod (SNP). SNP hamsters born from 4 wk before to 2 wk after the solstice underwent rapid somatic and gonadal growth; among those born 4-6 wk after the solstice, some delayed puberty by many weeks, whereas others manifested early puberty. Hamsters born eight or more weeks after the solstice failed to undergo early testicular development. The transition to delayed development occurred at long day lengths, which induce early puberty when presented as static photoperiods. The first animals to delay puberty may do so predominantly on the basis of postnatal decreases in day length, whereas in later cohorts, a comparison of postnatal day length to gestational day length may contribute to arrested development. Despite differences in timing of birth and timing of puberty, autumn gonadal regression and spring gonadal and somatic growth occurred at similar calendar dates in all cohorts. Incrementally changing photoperiods exert a strong organizing effect on seasonal rhythms by providing hamsters with a richer source of environmental timing cues than are available in simple static day lengths.     

Cancer incidence rate ratios of Turkish immigrants in Hamburg,Germany: A registry based study

The aim of this study was to estimate cancer incidence rate ratios for Turkish migrants in Hamburg, Germany. We used a name-based approach and identified 1346 cases with Turkish names (as a proxy of Turkish origin) among 140,249 cases of cancer registered in the cancer registry Hamburg during 1990–2005. To estimate the size of the denominator population, we applied the name-based approach to the population of Hamburg as well. The cancer incidence of specific cancer sites was compared between Turkish and non-Turkish cases using incidence rate ratios (IRR), stratified by gender and birth cohort. Our main findings are that cancer of the respiratory organs is diagnosed less frequent among Turkish men in older birth cohorts but with higher frequency in the younger birth cohorts. Malignant neoplasms of lymphoid, haematopoietic and related tissues are slightly higher in most male Turkish men birth cohorts, and even considerably higher for the birth cohort 1961 to <1971 (IRR = 1.8). Among women, incidence rates for Turkish women are lower than for non-Turkish women for cancer of the respiratory system, skin cancer and cancer of genital organs. Also, breast cancer incidence rates of Turkish women are lower than for non-Turkish women, especially in older birth cohorts. Incidence rate ratios of neoplasms of lymphoid, haematopoietic and related tissues are low in the 1931 to <1941 cohort (IRR = 0.71) but increase in younger birth cohorts. In conclusion, we found differences in cancer risks between cases with and without Turkish names for specific cancer sites. These results are consistent with the findings of studies from other countries.     

Developmental plasticity as a cohesive evolutionary process between sympatric alternate-year insect cohorts

Many species, particularly insects, pass through a series of distinct phases during their life history, with the developmental timing directed towards appropriate resources. Any factor that creates variation in developmental timing may partition a population into discrete populations-or 'cohorts'. Where there is continued failure to recruit outside the natal cohort then alternate cohorts will have their own internal dynamics, eventually leading to independent demographic and evolutionary trajectories. By contrast, continued variation in development rates within a cohort-cohort splitting-may homogenise otherwise independent demographic units. Using a panel of 14 microsatellite loci, we quantify the genetic signature of apparent demographic isolation between coexisting, but alternate, semivoltine cohorts of the damselfly Coenagrion mercuriale at locations that span its distribution in the UK. We find consistently low levels of genetic divergence between sympatric cohorts of C. mercuriale, indicative of developmental plasticity during the larval stage (unregulated development) whereby some individuals complete their development outside the predominant 2-year (semivoltine) period. Thus, individuals that alter their developmental rate successfully recruit to a different cohort. Despite maintaining contrasting population sizes, gene flow between alternate cohorts broadly is sufficient to place them on a similar evolutionary trajectory and also buffers against loss of genetic diversity. Such flexible larval development permits a response to local conditions and may facilitate response to environmental change.     

Gender differences in body build and physiological functions in the adult population of Yucatan, Mexico

This study, conducted in 1994-95, evaluates differences in body build, blood pressure and respiratory functions between sexes and age groups of low socioeconomic strata individuals living in Merida, Yucatan, Mexico. The cross-sectional sample includes 344 males and 320 females, 20-98 years of age divided into six age groups (20-29, 30-39, 40-49, 50-59, 60-69 and 70+ years) by sex. Differences between age cohorts in height, weight, fatness, systolic blood pressure, and most respiratory variables (excluding expiratory reserve volume, minute ventilation and respiration rate) are greater among women than in men. The more marked secular trend in stature and bigger biological differences between age cohorts in women might have its beginning in 19th century when living conditions of women were worse than those of men. Only since the last decades of 20th century, migrations and improvements in living conditions might caused more drastic changes in women of low social strata than in men. Results of regression analysis show a greater relationship between studied variables in women than in men what confirms that women are less sensitive to environmental factors. A pattern of changes in minute ventilation (MV) with rising age of the cohorts differs between men and women (smaller differences appear in the women's cohort) Also a different pattern (MV) is seen in European populations. The latter may suggest existence of some adaptational phenomena to the local environment.     

Radiation effects on breast cancer risk: a pooled analysis of eight cohorts

Breast cancer incidence rates after radiation exposure in eight large cohorts are described and compared. The nature of the exposures varies appreciably, ranging from a single or a small number of high-dose-rate exposures (Japanese atomic bomb survivors, U.S. acute post-partum mastitis patients, Swedish benign breast disease patients, and U.S. infants with thymic enlargement) to highly fractionated high-dose-rate exposures (two U.S. tuberculosis cohorts) and protracted low-dose-rate exposure (two Swedish skin hemangioma cohorts). There were 1,502 breast cancers among 77,527 women (about 35,000 of whom were exposed) with 1.8 million woman-years of follow-up. The excess risk depends linearly on dose with a downturn at high doses. No simple unified summary model adequately describes the excess risks in all groups. Excess risks for the thymus, tuberculosis, and atomic bomb survivor cohorts have similar temporal patterns, depending on attained age for relative risk models and on both attained age and age at exposure for excess rate models. Excess rates were similar in these cohorts, whereas, related in part to the low breast cancer background rates for Japanese women, the excess relative risk per unit dose in the bomb survivors was four times that in the tuberculosis or thymus cohorts. Excess rates were higher for the mastitis and benign breast disease cohorts. The hemangioma cohorts showed lower excess risks suggesting ameliorating dose-rate effects for protracted low-dose-rate exposures. For comparable ages at exposure (approximately 0.5 years), the excess risk in the hemangioma cohorts was about one-seventh that in the thymus cohort, whose members received acute high-dose-rate exposures. The results support the linearity of the radiation dose response for breast cancer, highlight the importance of age and age at exposure on the risks, and suggest a similarity in risks for acute and fractionated high-dose-rate exposures with much smaller effects from low-dose-rate protracted exposures. There is also a suggestion that women with some benign breast conditions may be at elevated risk of radiation-associated breast cancer.     

Socioeconomic and seasonal variations in births: A replication

Many studies, but not all, suggest that immigrant health worsens with duration of residence in the United States. Cohort effects may explain the inconsistent findings; not only are cohort effects confounded with duration, but the timing of entry into the United States may also create qualitatively different migration experiences. The present study tests for duration and cohort patterns among Asian immigrants to the United States across six year-of-entry cohorts (pre-1980, 1981–85, 1986–90, 1991–95, 1996–2000, 2001–05). Data come from the Asian American sample (n = 44,002) of the 1994–2009 waves of the National Health Interview Survey. The data show cohort differences for self-rated health, such that more recent cohorts showed improved baseline health compared to older cohorts. After accounting for cohorts, there was no significant change in self-rated health by duration of residence. Older cohorts actually showed improving self-rated health with longer duration. Obesity showed the opposite pattern; there were no differences across cohorts, but duration in the United States correlated with higher obesity. These results imply that immigrant health is not simply an issue of duration and adaptation; instead, they underscore the utility of considering cohorts as broader contexts of migration. Collectively, the results encourage future research that more carefully examines the etiological mechanisms that drive immigrant health.     

Children who acquire HIV infection perinatally are at higher risk of early death than those acquiring infection through breastmilk: a meta-analysis

BACKGROUND: Assumptions about survival of HIV-infected children in Africa without antiretroviral therapy need to be updated to inform ongoing UNAIDS modelling of paediatric HIV epidemics among children. Improved estimates of infant survival by timing of HIV-infection (perinatally or postnatally) are thus needed. METHODOLOGY/PRINCIPAL FINDINGS: A pooled analysis was conducted of individual data of all available intervention cohorts and randomized trials on prevention of HIV mother-to-child transmission in Africa. Studies were right-censored at the time of infant antiretroviral initiation. Overall mortality rate per 1000 child-years of follow-up was calculated by selected maternal and infant characteristics. The Kaplan-Meier method was used to estimate survival curves by child's HIV infection status and timing of HIV infection. Individual data from 12 studies were pooled, with 12,112 children of HIV-infected women. Mortality rates per 1,000 child-years follow-up were 39.3 and 381.6 for HIV-uninfected and infected children respectively. One year after acquisition of HIV infection, an estimated 26% postnatally and 52% perinatally infected children would have died; and 4% uninfected children by age 1 year. Mortality was independently associated with maternal death (adjusted hazard ratio 2.2, 95%CI 1.6-3.0), maternal CD4<350 cells/ml (1.4, 1.1-1.7), postnatal (3.1, 2.1-4.1) or peri-partum HIV-infection (12.4, 10.1-15.3). CONCLUSIONS/RESULTS: These results update previous work and inform future UNAIDS modelling by providing survival estimates for HIV-infected untreated African children by timing of infection. We highlight the urgent need for the prevention of peri-partum and postnatal transmission and timely assessment of HIV infection in infants to initiate antiretroviral care and support for HIV-infected children.     

Canadian fertility trends in perspective

This paper examines the broad movements of Canadian period and cohort fertility over the past 100 years, and compares them with corresponding trends in the US and other industrialized countries. The main movement in Canada was a decline in fertility extending from the 19th century to the present, interrupted in the 1940s and 1950s by a baby boom. Between 1871 and 1937 the total fertility rate (TFR) fell at about an average of 1.4% annually. The rate of fall in the US was similar, with the result that in the late 1930s the Canadian TFR was about 20% that of the US. The fertility boom that followed was steeper in the US than in Canada, and in the downswing that later followed, the rate of decline was similar in the 2 countries (3.4-4% annual average). But, the decline continued longer-- indeed still continues--in Canada, whereas the TFR in the US reached its lowest point in 1976. Moreover, the recent decline in fertility has been more severe in Canada than in almost any other industrialized country. The TFR relates to fertility in a single year and is highly sensitive to short-term changes in the timing of births. For the purposes of understanding and explaining long-term trends in fertility, the completed fertility rate (CFR) is a better index because it measures the ultimate family size of cohorts. Cohort fertility can be seen to fluctuate much less than does period fertility. In both the US and Canada, the peak cohorts, born in the early 1930s, had roughly the same completed fertility, and later cohorts continued to remain closely in step as the CFR fell sharply. In Canada the fall continues, though at a reduced rate, in the latest cohorts for which there is information. Apart from differences in amplitude, the dates of turning points and the shapes of the TFR and CFR curves of Canadian fertility are fairly similar. The long decline in cohort fertility is largely explained by the decrease in the proportions of families of 6 or more children. During the baby boom, for Catholics and non-Catholics alike, the proportion of ever-married women remaining childless fell by about 40%, the proportion having 2 children changed little, and the proportions having 3,4 and 5 children tended to increase substantially. The crucial difference between the 2 groups was in the proportions of women having 6 or more children. For non-Catholics, the proportion fell by over 4% from a high level. For non-Catholics, on the other hand, the proportion rose somewhat, though even after the rise, it was barely more than 1/2 the level to which the Catholic proportion had declined. Among Catholics, the effect of the massive decline in the proportion of women having 6 or more children was to swamp the effects of the increase in the proportions of women having 3, 4 and 5 children. The net effect was that fertility declined. Among non-Catholics, however, the comparable increases in the proportions of families of 3, 4 and 5 children, were not offset by any fall in the proportion of larger families, with the result that a baby boom occurred.     

Differential fertility in the United States, 1980: continuity or change?

This paper considers how changes in women's sociocultural characteristics have influenced recent patterns of differential fertility in the US and whether the convergence of fertility differentials observed up to 1970 has continued. The data are drawn from the June 1980 US Current Population Survey, which is a probability sample survey selected to represent the civilian non-institutionalized population living in households. The study population consists of 20,621 ever-married White and Black women aged 25-44, a group for various reasons considered to have a high impact from the point of view of fertility behavior. Fertility to date and ever expected fertility are the dependent variables. The respondents were separated into age cohorts, and differentiated by race. The data suggest that there has been no change in differential fertility in recent years: the 2 youngest cohorts (25-29 and 30-34 years) have similar expected fertilities that are lower than those of the older cohorts. Age at 1st birth, length of 1st birth interval, income, and education were negatively associated with fertility, among both older and younger women, of both races. Differentials by race have narrowed slightly. When fertility expectations were examined, the association of the independent variables with expected completed fertility was weaker among younger women, indicating that there has been some convergence in expected fertility. Further narrowing of differentials in actual fertility depends on how successful the younger women are in preventing future unplanned births. If the present tendency towards surgical sterilization (among both races and groups above and below the poverty level) persists, it will make it possible for more women to stay within their expected total fertility levels.     

The smoking epidemic across generations,genders, and educational groups: A matter of diffusion of innovations

This study determines whether the temporal variations in smoking habits across generations and genders and among groups with differing levels of education fit the pattern proposed by the theory of the diffusion of innovations (TDI) (Rogers, 2003). We focus on the Italian case and employ a pseudo-panel derived from repeated cross-sections of the annual household survey, “Aspects of Daily Life,” that was part of the Multipurpose Survey carried out by the Italian National Statistical Office (ISTAT) for the period 1997 to 2012. The results confirm Rogers’ TDI and show that smoking prevalence has declined over time and across age cohorts: Younger men of all educational levels and women with higher education are less likely to smoke than are those in other cohorts, while less-educated women who entered the smoking-diffusion process later than others are more likely to smoke. Hence, socio-economic differences in smoking continue to persist, especially for women. According to Rogers’ TDI, smoking prevalence is expected to continue to decline, particularly among little-educated women.     

Evidence for the retention of genetic variation in Erodium seed dormancy by variable rainfall

Summary The periodic occurrence of summer/early autumn precipitation in the California annual grassland can result in the formation of early and late emerging cohorts of Erodium botrys and E. brachycarpum. The occurrence of early rainfall and the timing of such rainfall are highly variable from year to year. A series of field watering experiments in 1980–81 were used to simulate early emergence conditions that would result from significant rainfall (1 cm) occurring in mid-July, late August, and mid-September. Net reproduction was used to estimate fitness differentials between Erodium cohorts emerging in response to a watering treatment (early emerging cohorts) and Erodium cohorts emerging with the onset of winter rains in mid-October (late emerging cohorts). Survival was lower and gross reproduction was higher among early emerging cohorts than late emerging cohorts. For both species, net reproduction of the early cohort was lower than that of the late cohort under the July watering treatment and higher than that of the late cohort under the August watering treatment.Early cohorts, formed in response to rainfall in mid-September, 1982, were also compared demographically to later cohorts emerging in October. Compared to late cohorts, net reproduction, gross reproduction and survival were higher for the early cohorts.Common garden experiments indicate that differences in the duration of seed dormancy between the progenies of early and late emerging plants reflect a significant genetic component. Progency produced by early cohorts of E. brachycarpum from all three watering treatments possessed more extended seed dormancy than progeny of late cohorts. In E. botrys, progeny from early cohorts emerging in response to the July watering treatment were also more dormant than late progeny. In contrast, early cohorts of E. botrys emerging in response to the September watering treatment produced seed less dormant than seed produced by late cohorts. When combined with demographic data, indicating that fitness differentials between early and late cohorts varied with changes in the date of early emergence, genetic results suggest that year to year variation in early rainfall may act to retain genetic variation in the duration of seed dormancy.     

Recruitment in Japanese sea bass,Lateolabrax japonicas (Cuvier, 1828): effects of timing on spawning and larval quality and quantity

This study aimed to elucidate the causes of variability in larval survival and juvenile abundance (recruitment) within and among cohorts of Japanese sea bass (JSB; Lateolabrax japonicus), a winter‐spawning temperate coastal marine fish. Larvae and settled individuals (settlers) belonging to four cohorts were collected from Tango Bay (the Sea of Japan coast) during eight sampling cruises in 2007 and 2008. Larvae were sampled in January and February each year using an ichthyoplankton net, and settlers were collected in February and March each year using a beam trawl. Age of individual larva and settlers was determined and growth history was back‐calculated from otolith microstructure, and the hatch date distribution was computed. Temperature, daily growth rate, size‐at‐age, hatch date, and density data of larvae and settlers allowed elucidating the effects of the timing of spawning and larval quantity and quality (growth rate and body size) on larval survival and recruitment within and among cohorts of JSB. Results showed that cohorts that hatched earlier in the season had higher quantity of larvae, experienced higher mean temperatures and survived better than cohorts hatched later. Recruitment variability among cohorts is determined largely by the initial quantity of larvae, as this explained >97% of the variability in recruitment among cohorts. Within cohorts, larger hatched larvae grew faster than their smaller conspecifics, and the bigger and faster growing larvae survived and settled. Results from this study suggest the following scenarios for recruitment of JSB: (i) earlier spawning in the season promotes larval survival since earlier cohorts are likely to encounter a better temperature and perhaps food conditions, and therefore recruit better than later cohorts; (ii) the initial quantity of larvae appears to be an important determinant of recruitment variability among cohorts; and (iii) the size‐ and growth‐related mechanisms operating during the larval phase appear to start at the time of the hatch.     

Gender differences in HIV-1 diversity at time of infection

To develop an HIV-1 vaccine with global efficacy, it is important to identify and characterize the viruses that are transmitted, particularly to individuals living in areas of high incidence. Several studies have shown that virus from the blood of acutely infected adults was homogeneous, even when the virus population in the index case was genetically diverse. In contrast to those results with mainly male cohorts in America and Europe, in several cases a heterogeneous virus population has been found early in infection in women in Africa. Thus, we more closely compared the diversity of transmitted HIV-1 in men and women who became infected through heterosexual contact. We found that women from Kenya were often infected by multiple virus variants, whereas men from Kenya were not. Moreover, a heterogeneous virus was present in the women before their seroconversion, and in each woman it was derived from a single index case, indicating that diversity was most likely to be the result of transmission of multiple variants. Our data indicate that there are important differences in the transmitted virus populations in women and men, even when cohorts from the same geographic region who are infected with the same subtypes of HIV-1 are compared.     

Migration,socio-economic status and age at menarche and age at menopause in the Yucatan,Mexico

The possible effects of migration and socio-economic status (SES) on age at menarche (MENA), age at menopause (MENO), potential reproductive period (PRP), and the correlation between MENA and MENO, were studied in 216 women in the Yucatan, Mexico. They were divided into three groups: migrant from the sisal-growing area on the coast, and sisal and coastal sedentary. Coastal sedentary women, living in the best socio-economic conditions, have the youngest MENA and the oldest MENO. Early migrant women have a significantly younger MENO (p.<0.05) and shorter PRP than Coastal sedentary women. There was no evidence of selective migration for MENA. When the Migrant, Sisal and Coastal sample were divided into cohorts by SES, it was impossible to obtain any clear picture. MENA increases with increased SES for the Coastal and Sisal cohorts, while the Migrant cohorts show an opposite trend. However, only the Low/Middle and High/Middle cohort differences for the Coastal sample are significant (p.<0.05, in both cases). It seems that migration has a limited affect on MENO and the PRP. Contrary to reports in the literature, the correlations between MENA and MENO and migrant status, and migrant socio-economic statuses, are negative, although these correlations were statistically significant in the Coastal sample.