Distribution Of Birth Intervals Research Articles

Monthly Estimates of the Quantum of Fertility: Towards a Fertility Monitoring System in Austria

Short-term variations in fertility and seasonal patterns of childbearing have been of interest to demographers for a long time. Presenting our detailed study of period fertility in Austria since 1984, we discuss the problems and advantages of constructing and analysing various period fertility indicators that reflect real exposure and potentially minimise the distortions caused by changes in fertility timing. We correct monthly birth data for calendar and seasonal factors and show that seasonality of births in Austria varies by birth order. Our study reveals that the methods explicitly aimed at adjusting fertility rates for tempo distortions are not suitable for computing monthly fertility rates. However, most of the timing distortions can be eliminated when using an indicator derived from the period parity progression ratios based on birth interval distributions, termed the Period Average Parity (PAP). We illustrate the insights gained from PAP and compare it with the commonly used total fertility rates in an analysis of the recent upswing in period fertility, starting in the late 2001. This investigation will serve for establishing a monitoring of monthly fertility rates in Austria.

Trend of determinants of birth interval dynamics in Bangladesh.

BackgroundThe distribution of birth intervals can be used to draw attention to important characteristics of dynamics of fertility process. The main objective of this paper is to examine the effects of socioeconomic, demographic and proximate determinants on the length of birth intervals of women of Bangladesh and also to see whether the effects are changed over the years.MethodsBirth intervals can be considered as correlated time-to-event data because two or more birth intervals could correspond to a single mother. Moreover, women from the same neighborhood usually share certain unobserved characteristics, which may also lead to correlated time-to-event data (birth interval). A parametric random effect (frailty) model is used to analyze correlated birth interval data obtained from three Bangladesh Demographic and Health Surveys (BDHS 2004, 2007, and 2011).ResultsThe results show that alongside different socioeconomic, demographic determinants, unobserved community and mother effects have considerable impact on birth interval in Bangladesh. However, the effects of different factors on birth interval changes in a small scale over the duration of 2004–2011.ConclusionsEfficient policy is a priority for promoting longer birth spacing and achieving a decline in fertility.

Monthly Estimates of the Quantum of Fertility: Towards a Fertility Monitoring System in Austria

Short-term variations in fertility and seasonal patterns of childbearing have been of interest to demographers for a long time. Presenting our detailed study of period fertility in Austria since 1984, we discuss the problems and advantages of constructing and analysing monthly series of various period fertility indicators that reflect real exposure and potentially minimise the distortions caused by changes in fertility timing. We correct monthly birth data for calendar and seasonal factors and show that seasonality of births in Austria varies by birth order. Our study suggests that most of the timing distortions can be eliminated when using an indicator derived from the period parity progression ratios based on birth interval distributions, termed the “period average parity” (PAP). We illustrate the insights gained with the PAP and compare this with the commonly used total fertility rates in an analysis of the recent upswing in period fertility, starting in the late 2001. This investigation will be useful in establishing a monitoring of monthly fertility rates in Austria.

Whose Reality? Local Perceptions of Fertility Versus Demographic Analysis

Single-round demographic surveys of three Malian populations showed substantial fertility differentials, with much lower fertility in the two nomadic pastoral Kel Tamasheq populations than among the sedentary cultivating Bambara. Demographic analysis explained these fertility differentials by different marriage patterns, dominated by the structural effects of Kel Tamasheq monogamy which maintains a large group of currently unmarried women. This contrasts with the Kel Tamasheq's own pre-occupations with their low fertility which they ascribe to pathologically induced subfecundity and sterility. Parity progression ratios and birth-interval distributions are used to examine the degree to which the Tamasheq perceptions of their own fertility behaviour can be demonstrated by using the demographic data. The importance of the different perspectives and outcomes is discussed, with the need for taking into account local concerns both in analysis and ultimate policy interventions.

Birth spacing patterns in humans and apes

Comparative studies of birth interval dynamics in wild primates suffer from several problems of analysis and interpretation: (1) the data are always right-censored, (2) sample sizes are usually small, (3) the distribution of birth intervals is expected to be non-normal, (4) early offspring mortality is a confounding variable, and (5) differences in life history (e.g., presence or absence of menopause) can complicate interpretation of the results. A survival analysis designed to minimize these problems is applied to published data on wild chimpanzees and gorillas from Gombe and Virunga Parks, respectively, and to new data on wild orangutans from Tanjung Puting National Park and on a human population, the Gainj of highland Papua New Guinea. According to this analysis, the estimated median birth interval (when the offspring whose birth opens the interval does not die within the interval) is 43.3 +/- 1.0 months for the Gainj, 45.5 +/- 1.2 months for gorillas, 66.6 +/- 1.3 months for chimpanzees, and 92.6 +/- 2.4 months for orangutans.

Period parity progression ratios and birth intervals in England and Wales, 1941-1971: a synthetic life table analysis.

A method is presented for analysing maternity history data to provide period estimates of parity progression ratios, birth intervals and related indices. This is applied to a sample of the marriage and maternity histories from the Census of England and Wales of 1971 and shows: (a) a general increase through the 1950s and into the 1960s in period estimates of marriage and parity progression ratios, especially in the progression from first to second birth; (b) a general acceleration of fertility with, again, the second birth interval becoming particularly short and compact; and (c) very steep declines in third and fourth birth progression ratios from the mid-1960s. Birth interval distributions altered during the period examined. Decomposition of a progression-based total fertility index shows change in the ratios for lower birth orders to have dominated the fertility upswing and declines in ratios for higher birth orders to have initiated the subsequent decline.

Breastfeeding, Contraception, and Birth Intervals in Developing Countries

Numerous studies have demonstrated a strong correlation between breastfeeding and the duration of amenorrhea and between breastfeeding and the birth interval at the individual level. In the present study, both these correlations are shown to hold at the national level, in developing countries. In countries where the median durations of breastfeeding are relatively long or the rates of contraceptive use are relatively high, median birth intervals are longer than in countries where the median breastfeeding durations are shorter and contraceptive use is less widespread. In countries where fertility is moderate or high, however, the incidence of very short birth intervals is higher when median breastfeeding durations are relatively short. The findings suggest that contraception as it is presently practiced is an inadequate substitute for breastfeeding.

Birth spacing and fertility limitation: a behavioral analysis of a nineteenth century frontier population

Our analysis of changing birth interval distributions over the course of a fertility transition from natural to controlled fertility has examined three closely related propositions. First, within both natural fertility populations (identified at the aggregate level) and cohorts following the onset of fertility limitation, we hypothesized that substantial groups of women with long birth intervals across the individually specified childbearing careers could be identified. That is, even during periods when fertility behavior at the aggregate level is consistent with a natural fertility regime, birth intervals at all parities are inversely related to completed family size. Our tabular analysis enables us to conclude that birth spacing patterns are parity dependent; there is stability in CEB-parity specific mean and birth interval variance over the entire transition. Our evidence does not suggest that the early group of women limiting and spacing births was marked by infecundity. Secondly, the transition appears to be associated with an increasingly larger proportion of women shifting to the same spacing schedules associated with smaller families in earlier cohorts. Thirdly, variations in birth spacing by age of marriage indicate that changes in birth intervals over time are at least indirectly associated with age of marriage, indicating an additional compositional effect. The evidence we have presented on spacing behavior does not negate the argument that parity-dependent stopping behavior was a powerful factor in the fertility transition. Our data also provide evidence of attempts to truncate childbearing. Specifically, the smaller the completed family size, the longer the ultimate birth interval; and ultimate birth intervals increase across cohorts controlling CEB and parity. But spacing appears to represent an additional strategy of fertility limitation. Thus, it may be necessary to distinguish spacing and stopping behavior if one wishes to clarify behavioral patterns within a population (Edlefsen, 1981; Friedlander et al., 1980; Rodriguez and Hobcraft, 1980). Because fertility transition theories imply increased attempts to limit family sizes, it is important to examine differential behavior within subgroups achieving different family sizes. It is this level of analysis which we have attempted to achieve in utilizing parity-specific birth intervals controlled by children ever born.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysing open birth interval distributions

Summary This paper began with the recognition that open birth interval distributions are analogous to age distributions. It then became clear that closed birth interval distributions are, somewhat more loosely, analogous to mortality schedules, and that the relationship between open and closed birth interval distributions could be explored by imitating the formal demography of mortality and age distribution. Pursuing this programme, we develop the formal demography of open and closed birth interval distributions and show that under certain assumptions open interval distributions may be used to estimate closed interval distributions, just as age distributions may be used to estimate mortality. An illustrative application to Indonesian data is given.

Population dynamics based on birth intervals and parity progression

Abstract The Chinese population policy of 'later-longer-fewer' suggests a formulation of population dynamics in terms of birth intervals and parity progression. This leads to population projections based on birth interval distributions and parity progression ratios and to an alternative to Lotka's stable population theory in which age is replaced by parity and interval since last birth. A numerical comparison with Lotka's model indicates similarities and differences between the two approaches: The formulation suggests an approach to the analysis of birth interval and parity progression statistics that effectively solves censoring and selection problems.

Parity patterns of birth interval distribution

A simplified model is presented for the measurement of inter-live birth interval distributions. Comparative analyses of "effective fecundability," the mean length and variation of postpartum infecundity, and the parity progression ratio based on this measurement model are presented using data from U.S. marriage cohorts and from an Indian sample. Parity differentials in these reproduction parameters are investigated, and the ramifications for fertility estimate and projection discussed.

Distribution of birth intervals according to the sampling frame

Observed distributions of the lengths of intervals between successive births (or of the open intervals since the most recent birth) are considerably affected by: (i) the sampling frame, which includes the method of ascertaining persons to be investigated and the kind of data obtained from each individual, (ii) the composition of the population sampled, and (iii) the effects of competing risks of such events as death, marriage, marital dissolution and the ending of previous intervals. Some of these factors also affect distributions of other duration variables such as age (at death or some point in time) marital duration, length of residence, etc. Estimates of birth intervals are complicated both by their dependence upon marital duration and survival and by the diversity of sampling frames which are realistically feasible or desirable.

The distribution of birth intervals under a class of stochastic fertility models

Abstract Characterization ofthe distribution ofintervals between successive births affords both practical and theoretical advantages in the analysis of fertility data. Moreover, attempts to formulate a mathematical model describing the process of reproduction lead naturally to a consideration of the distribution of birth intervals. A class ofmodels has been formulated, applying to a woman who is not pregnant and fecundable at marriage and who after a variable length of time enters a pregnancy, which terminates in either a miscarriage, stillbirth, or live birth, with a given probability depending on the duration of the pregnancy. Each pregnancy is followed by a period of post-partum infecundability (physiological sterility), whose length depends on the outcome of the pregnancy. Eventually, the woman returns to the non-pregnant fecundable state. The durations of pregnancy and of post-partum infecundability are treated as variables whose distributions can depend on the next state (such as the outcome ofpregnancy) as well as on the state being currently occupied. Expressions for the mean and variance of the intervals to the first live birth and the intervals between subsequent live births, as based on this formulation, are given. With the aid of numerical examples, these characteristics of the birth intervals are examined, particularly with respect to the effects of including terms for foetal deaths in the model. The mean length and the variance of the intervals increase with the frequency offoetal death and the duration of the associated infecundable periods. Generally, the variance of birth intervals is greater than expected from estimates in which the occurrence of foetal deaths is ignored. For intervals after the first, similar mean values may result either from a lowered fecundability (probability of conceptio) or from an increase in the duration of post-partum physiological sterility. If this change resulted from a decreased fecundability the variance of the birth intervals would be much greater than if the change were due to prolongation of post-partum infecundability. Applications ofthese results are possible even in the absence of reliable data for the frequency of foetal deaths.

The Distribution of Birth Intervals Under a Class of Stochastic Fertility Models

The Distribution of Birth Intervals Under a Class of Stochastic Fertility Models