Flux induced biochemical differentiation.

Any realistic model of human fertility should encompass the distributions and interactions of three time intervals a fecund married woman may experience repeatedly in her childbearing period: (1) waiting time for a conception, (2) gestation period, and (3) period of postpartum amenorrhea. Perrin &; Sheps (1964) presented a model in which human reproduction is viewed as a Markov renewal process with a finite number of states. Das Gupta (1973b) presented a general probability model of fertility along the lines suggested by Perrin &; Sheps which removes two limitations of their model. First, it does not assume that the distributions of durations of stay in the fertility states are independent of each other. Second, it allows us to study the effect of breast-feeding on demographic characteristics, such as interval between live births or birth rate. Results derived in Das Gupta (1973b) include the distributions of time intervals and the exact probabilities of different states at a particular time. The present paper includes additional results pertaining to the same general model, such as the distribution of number of conceptions in a fixed period of time, the distribution of time needed for a fixed number of conceptions, pregnancy rate and fertility rate, and the distribution of the time elapsed since last live birth. The general results are applied to specific models to obtain some known results.     

A stochastic model of human reproduction: some preliminary results

The stochastic model of human reproduction presented in this paper removes some of the limitations of the Perrin—Sheps model. It considers the possibility of dependence of amenorrhea period on the preceding gestation period, and also for live births, on the breast-feeding practices of the mother. Two models, virtually identical in concepts, are considered depending on whether time is treated as a continuous or discrete variable. The basic distributions in the models are kept arbitrary, and, therefore, the results for all the existing homogeneous fertility models can be obtained directly from the general results as special cases. The results presented here include the distribution of the interval between two live births, and the probabilities of different states at a point in time. We also illustrate the applications of the models to special cases and generate many known results.     

A study of a Malthusian parameter in relation to some stochastic models of human reproduction

The paper is divided into six sections and is devoted to a study of a Malthusian parameter in relation to some stochastic models of human reproduction. In Section 1, some of the motivations underlying the study are discussed, and in Section 2 some literature on the stochastic model of population growth underlying the foundations of the paper is briefly reviewed. Section 3, which lays the foundations for the study of a more complicated model in Section 4, is devoted to the study of the Malthusian parameter in relation to a stochastic model of human reproduction formulated as a terminating renewal process. In Section 4 the Malthusian parameter is studied in relation to a terminating Markov renewal model of human reproduction, stemming from the work of Perrin and Sheps (1964). Among the mathematical results of independent interest in this section is a complete spectral decomposition of the Laplace-Stieltjes transform of the semi-Markov transition matrix in the model of Perrin and Sheps. Section 5 is devoted to the discussion of a mathematical method which allows accomodating in the model the time taken by an individual to reach reproductive age, and Section 6 ends the paper by supplying bounds for the Malthusian parameter which are valid under quite general conditions. Possible applications of the results in evaluating what influences a population policy may have on population growth are also discussed.     

On the convergence of Das Gupta's model of fertility projection.

A regression model expressing the age-specific fertility rates at a given point of time as a variable dependent upon the same at the preceding points of time has been developed by Das Gupta for purposes of fertility projection. The model, judged by the values of the multiple correlation coefficients, appears to work very well with the U.S. data set, and it also produces limiting values of the fertility rates when the projection is carried far into the future. The conditions of convergence of such a model have been determined in this paper according to which the model's usefulness for purposes of long-term projection of fertility rates appears to be severely restricted.     

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.     

Birth seasonally among peasant cultivators: The interrelationship of workload,diet, and fertility

The monthly distribution of live births was analyzed over a 51-year period, 1926–1976, for a rural Taiwan fishing community. Unlike previous studies of birth seasonality, monthly distributions of births did not deviate from what would be expected by chance. This new case is shown to be consistent with the suggestion, developed by Pasternak during a study of birth seasonality in two Taiwan farming communities, that for peasant cultivators the annual cycle of production exerts a more decisive influence on birth seasonality than time of marriage or attributes of temperature, rainfall, or workload. An hypothesis that links the productive cycle to conceptions through the intervening variable of diet is presented and successfully tested using several sets of data on monthly births. A direct effect of nutrition on human fertility, suggested by recent studies of reproductive performance under conditions of nutritional stress, may largely explain seasonality of conceptions and births in populations that experience significant seasonal variation in diet.The Cross Harbor data presented in this paper were collected as part of an ongoing investigation of the comparative demography and social structure of fishing, farming, and market town communities located within a particular Chinese regional system. The support of the National Science Foundation during the period of fieldwork is gratefully acknowledged. I wish to thank G. William Skinner, William H. Durham, Greg Acciaioli, Steven Sangren, Chuang Miao-huei, Harumi Befu, and Philip L. Ritter for their comments on earlier drafts of the present article. I owe a special debt of gratitude to Burton Pasternak (City University of New York), who intellectually inspired and personally encouraged the writing of this paper.     

Seasonality of births in South-Eastern Nigeria.

A study of seasonal pattern of births in Nigeria was conducted using data on live births for the period 1971-76 from 4 climatically similar southeastern states (Anambra, Imo, Cross River and Rivers State). After pooling the data, the monthly distribution for different years was calculated. The resulting time series was graphically compared with temperature levels during time of conception, or nine months back. Data analysis revealed a seasonal pattern in the monthly distribution of births, with the peak period observed during April-June, and a trough during November-January. Counting 9 months back, the conceptions were calculated as occuring during July, August, or September of the previous year. In terms of the annual agricultural cycle of the southeastern states, July-September corresponded with the period of light farm work or relative idleness for men (main activity during this period is weeding and tending the crops, tasks primarily done by women and children); this is also a period of abundance of fruits, vegetables and palm wine, and rains after dusk, conditions conducive to mating.     

Herbivores and the Spatial Distributions of the Phytoplankton. I. The Plankton Market

Planktonic herbivores forage on phytoplankton cells which were produced at some earlier time and at a distant place. A steady state, one dimension model of the birth, death and eddy diffusion of phytoplankton illustrates phytoplankton smooth both temporal and spatial variations as they are transported. When the eddy diffusivity is k and the phytoplankton doubling time is b, the average distance traveled by a phytoplankton cell is (kb)^1/2 and the average time spent doing so is b. Only those spatial variations with wavelengths greater than 2π(kb)^1/2 and temporal variations with periods greater than 2πb will be observed in the phytoplankton distributions at more than half their original amplitude. Both k and b control the length scale of phytoplankton distributions in a cartesian coordinate system. Planktonic herbivores view the phytoplankton from a diffusing coordinate system in which the spatial scales of the phytoplankton distribution are transformed into time scales.     

A new name for Limnophyes montanus Chaudhuri,Sinharay & Das Gupta (Diptera: Chironomidae) from India

Limnophyes nigripes is proposed as a replacement name for Limnophyes montanus Chaudhuri, Sinharay & Das Gupta, nee Limnophyes montanus Goetghebuer.     

The spatial distribution of the wheat-bulb fly,Leptohylemyia coarctata (fall.) (Diptera: Anthomyiidae)

The spatial distribution of the eggs, larvae, pupae and adults of the wheat-bulb fly was investigated by fitting 42 sets of data comprising 1334 samples to the Poisson and negative binomial distributions, and by using the power law (S²=am^b). In general, the tests indicated that all stages were aggregated and fitted the negative binomial model.     

Sunshine,fertility and racial disparities

This research investigates the effect of sun exposure on fertility, with a special focus on how its effects and consequences for birth outcomes may differ by race. Sun exposure is a key mechanism for obtaining Vitamin D, but this process is inhibited by skin pigmentation. Vitamin D has been linked to male and female fertility and risk of miscarriage, and Vitamin D deficiency is more prevalent among blacks than whites. Using 1989–2004 individual live births data from the Natality Detail Files, county-level, monthly conceptions are estimated as a function of monthly solar insolation, temperature and humidity, as well as month, time and location fixed effects and controls. Insolation has positive, statistically significant effects on fertility for both non-Hispanic blacks and whites, but the effects are stronger and the pattern of effect different for black mothers than white mothers. Poisson estimates from the main model suggest that a 1 kWh increase in average daily insolation in the conception month – approximately the difference in sunshine experienced in the typical September vs. October – increases non-Hispanic black conceptions by 1% and non-Hispanic white conceptions by 0.6%. Allowing insolation's effect to differ by maternal characteristic suggests that the racial differences are not being driven by differences in socioeconomic status (SES). Models that allow for more complicated timing of insolation's effect further suggest that insolation pushes black (white) conceptions into the unfavorable (favorable) season of birth. These estimated effects and our decomposition analyses suggest that insolation – and the implied Vitamin D deficiency underlying its effect–helps explain why black conceptions are more likely to display a seasonal pattern that is disadvantageous to birth outcomes.     

A Study of Second Order Approximation of Some Ratio Type Strategies

For estimating the mean of a finite population using information on an auxiliary variable, the conventional ratio strategies and strategies due to Srivastava (1967), Reddy (1973), Gupta (1978), Sahai (1979) and Adhvaryu-Gupta (1983) have been studied. Asymptotic expressions for the second order approximations of biases and mean square errors of these strategies have been obtained. The suitability of these strategies have been discussed with the help of live data.     

Factors in the incidence of childlessness in Canada: An analysis of census data

The impact of the 1918 influenza pandemic on human fertility has been subject to significant scholarly debate. The current study characterizes the inter-temporal association between excess deaths during the pandemic and the subsequent birth deficit by identifying the length of time between these two phenomena using cross-correlations of monthly death and birth data from Taiwan from 1906 to 1943. The analysis demonstrates a strong and negative correlation between deaths (d) at time t and births (b) at time t + 9 (r_db(9) = –0.68, p < .0001). In other words, a significant drop in births was observed nine months after pandemic mortality peaked. The findings suggest that the 1918 influenza pandemic impacted subsequent births primarily through the mechanism of reduced conceptions and embryonic loss during the first month of pregnancy rather than through late-first-trimester embryonic loss.     

A probability model for the number of births in an equilibrium birth process

A probability model for the number of complete conceptions (that is, live births) taking into account foetal wastages, occurring in a couple during a specified period of time (T₀, T₀+T) is developed assuming that the data was collected starting a long time after marriage. A method of estimating some of the underlying parameters is given. The model is applied to data obtained in a Varanasi Survey in 1969–70.     

Besprechungen / Reviews

Book Reviewed in this article: Scourse , N. J. S., und R. A. Hinde (1973): Habituation to auditory stimuli in Mice (Wie Mäuse sich an akustische Reize gewöhnen). Kramer , D. L. (1973): Parental Behaviour in the Blue Gourami Trichogaster trichopterus (Pisces, Belontiidae) and its induction during exposure to varying numbers of conspecific eggs (Das Brutpflegeverhalten des Getüpfelten Guramis und seine Auslösung durch verschieden große Mengen arteigener Eier). Shallenberger , R. J., und W. D. Madden (1973): Luring behaviour in the Scorpion Fish Iracundus signifer (Wie I. s. Beutefische ködert). Chamove , A. S. (1973): Rearing infant Rhesus together (Das Verhalten miteinander aufgezogener Rhesusaffenkinder). Stamps , J. A., und G. W. Barlow (1973): Variation and stereotypy in the displays of Anolis aeneus (Sauria: Iguanidae) (Starrheit und Veränderlichkeit im Ausdrucksverhalten von A. ae.). Moodie , G. E. E., J. D. McPhail , und D. W. Hagen (1973): Experimental demonstration of selective predation on Gasterosteus aculeatus (Stichlinge sind als Beutefische auch im Versuch verschieden stark gefährdet). Maurus , M., und H. Pruscha (1973): Classification of social signals in Squirrel Monkeys by means of cluster analysis (Klassifizierung von Sozialverhaltensweisen des Totenkopfäffchens durch Gruppenanalyse). Wiley , R. H. (1973): The strut display of male Sage Grouse: a “fixed” action pattern (Das Stolzierverhalten männlicher Beifußhühner als “fixiertes” Verhaltensmuster). Sachs , L. (1972): Statistische Methoden. Ein Soforthelfer für Praktiker in Naturwissenschaft, Medizin, Technik, Wirtschaft, Psychologie und Soziologie. Bauer , H. Ch., R. Hofer , W. Knapp und H. Moser (1974): Zoologische Experimente. Kästle , W. (1974): Echsen im Terrarium. 2. Aufl. Reihe: Das Vivarium. Franckh'sche Verlagshandlung Stuttgart. Rensch , Bernhard, und Gerti Dücker (1973): Discrimination of patterns indicating four and five degrees of reward by birds (Vögel lernen vier bis fünf Bilder als Wertmarken für ebenso viele verschiedene Belohnungsstufen zu unterscheiden). Krall , Peter (1973): Der gesunde und der kranke Hund. 9. neubearbeitete Auflage von Georg Müller/Richard Reinhard: Der kranke Hund. Lawick , H. v. (1974): Solo; ein Hundeschicksal in der Serengeti. Verlag Ullstein GmbH, Frankfurt—Berlin—Wien.     

Distributions of coital rates and of fecundability

Abstract

Attempts have been made to fit distributions of conception waits on the assumption that fecundability is distributed as a Pearson Type I beta distribution. Since the fits were unsatisfactory (Majumdar and Sheps, 1970), the question arises whether fecundability is distributed as a Type III. If it were, then the probability of coitus should also be distributed as a Type III, and distributions of coital rates should be better fitted by the negative binomial than by Skellam's distribution. The data available for such fits have been briefly reviewed here and fits attempted. There is some slight evidence in favor of the hypothesis, but more data are needed before the question can be decisively answered.     

Eurotiaceae Trovate in Risaia

Abstract

Studying the mycological flora of paddy and grass-fields we had the opportunity to isolate some species of Eutotiaceae which are of particular interest. Three species were not yet known in Italy and only one was found in a soil of mountain pasture. The last one is also common in paddy fields. One of the isolated species was a Pseudoeurotium van Beyma, ascomycete with asci containing 16 ascospores, not identifiable with the systematically related species described as Pseudoeurotium indicum (Chattopadhyay and Das Gupta) Chattopadhyay from « oryzetis » in India and Pseudoeurotium multisporum (Saito and Minoura) Stolk in Japan. Some distinct morphological differences exist between our isolates and P. multisporum; but they differ only faintly from P. indicum: that is our isolates have pedicellate asci. Therefore we suggest the new variety: Pseudoeurotium indicum (Chattopadhyay and Das Gupta) Chattopadhyay var. orizetorum nobis. Three species of the genus Emericellopsis van Beyma: E. minima Stolk, E. terricola van Beyma and E. humicola (Cain) Cain were also isolated. The first one from the paddy-fields and the last two, not yet described in Italy, from grass fields. The possible relationship between E. minima Stolk arid E. pusilla Mathur, Sukapure and Thirumalachar has been discussed.     

Intraspecific application of the mid-domain effect model: spatial and temporal nest distributions of green turtles, Chelonia mydas, at Tortuguero, Costa Rica

The mid‐domain effect (MDE) model was developed to evaluate patterns of species richness. We applied the MDE model to intraspecific distribution patterns – the spatial and temporal nest distributions of green turtles, Chelonia mydas, at Tortuguero, Costa Rica, from 1972 to 2000. Spatial and temporal distributions of green turtle nests at Tortuguero did not exhibit significant annual variation over this time period. The spatial and temporal distribution of nests largely conformed to the predictions of the MDE model, although the spatial model has a better fit. Environmental factors that may cause deviations from the MDE model are discussed. The model also indirectly provided a first estimate of the mean spatial nesting range of individual green turtles at Tortuguero: 10.1 km (SD 8.7 km). The MDE model provides insight into intraspecific as well as interspecific distribution patterns.     

Exponentiated Exponential Family: An Alternative to Gamma and Weibull Distributions

In this article we study some properties of a new family of distributions, namely Exponentiated Exponential distribution, discussed in Gupta , Gupta , and Gupta (1998). The Exponentiated Exponential family has two parameters (scale and shape) similar to a Weibull or a gamma family. It is observed that many properties of this new family are quite similar to those of a Weibull or a gamma family, therefore this distribution can be used as a possible alternative to a Weibull or a gamma distribution. We present two real life data sets, where it is observed that in one data set exponentiated exponential distribution has a better fit compared to Weibull or gamma distribution and in the other data set Weibull has a better fit than exponentiated exponential or gamma distribution. Some numerical experiments are performed to see how the maximum likelihood estimators and their asymptotic results work for finite sample sizes.     

Hemoglobin genotype, fertility, and the malaria hypothesis

Epidemiological and clinical studies (Fleming et al. 1985; Perrin et al. 1982) indicate that hemoglobin (Hb) AS individuals have a selective advantage in malarial environments. Thus the high frequency of Hb S in human populations has been attributed to the decreased malarial morbidity and mortality experienced by Hb AS heterozygotes. It has also been suggested that Hb AS women have a higher fertility than that of Hb AA women, thus contributing to the elevated frequency of Hb S in malarial environments (Livingstone 1957). Firschein (1961) demonstrated a significantly greater fertility among Hb AS females, whereas Custodio and Huntsman (1984) documented no fertility differential between Hb AS and Hb AA women. Here I examine the reproductive careers of Hb AA and Hb AS subjects 40 years of age and older from Limon, Costa Rica. The purpose is to determine whether normal homozygotes and heterozygotes have significantly different fertilities. The research shows that these groups do not have significantly different completed family sizes (t = 0.38, ns) or significantly different numbers of pregnancies (t = 0.34, ns), live births (t = 0.36, ns), or abortions (t = 0.20, ns). My results support previous suggestions that differential fertility does not contribute to the maintenance of the Hb S polymorphism.