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This is a book review turned research paper. The aim is to estimate the differences in the maternal mortality rate (MMR) between untrained midwives, expert midwives, and the famous obstetrician Dr Smellie in eighteenth-century Britain. The paper shows that the birth attendance practices of the expert midwife Mrs Stone and of Dr Smellie were very similar, though Stone used her hands whereas Smellie used forceps. Both applied the same invasive techniques to successfully deliver women with similar fatal complications, techniques that untrained midwives and most surgeons of the time could not perform. However, the same procedures, if used for normal births, would have increased the MMR. So, the key to the low MMR of both was that they kept interventions away from the majority of births that were normal. The paper quantifies the likely MMR for a 'Stone and Smellie style' birth attendance and concludes that the wider dissemination of their techniques can explain the decline in the British MMR.

This paper explores the linkages at the family level between sustained high fertility and children's schooling in Ghana, in the context of a constrained economic environment and rising school fees. The unique feature of the paper is its exploration of the operational significance of alternative definitions of “sib size” – the number of “same-mother” siblings and “same-father” siblings – in relation to enrolment, grade attainment, and school drop-out for boys and girls of primary and secondary school age. The analysis is based on the first wave of the Ghana Living Standards Measurement Survey (GLSS) data, collected in 1987–88. The results of the statistical analysis lead to the conclusion that the co-existence of high fertility, rising school costs, and economic reversals is having a negative impact on the education of girls, in terms of drop-out rates and grade attainment. Some of the costs of high fertility are borne by older siblings (particularly girls) rather than by parents, with the result that chil...

This paper considers the impact of sample-attrition through dropouts on mortality analyses, using the pioneering IFORD survey of Yaounde (Cameroon). The essential issue in the IFORD surveys is the possibility that mortality of members of the cohort may differentially select some children, with specific underlying characteristics. The paper implements a method to assess the following three distinct concerns that may arise in the analysis of the IFORD data: (a) the estimation of the relationship between the covariates and the rate of occurrence of mortality or attrition over time; (b) the study of the interrelation between processes under a specific set of conditions during intervals between rounds for those children still alive and in the survey at the beginning of each interval; and (c) the issue of whether mortality and mortality differentials are affected when attrition is ignored. This approach accounts for sample-selection bias that may have resulted in the attrition process. The analyses provide insi...

While studies in high-income countries have shown that failure to achieve fertility desires is significantly associated with unfavourable personal circumstances, there is barely any empirical evidence on the factors that influence the pattern of unrealized fertility in sub-Saharan Africa. Using data from the 2018 Nigeria Demographic and Health Survey, this paper investigates the roles of ethnicity and the sex composition of living children on unrealized fertility in Nigeria. The results show that the odds of having unrealized fertility were higher among Hausa-Fulani women compared with women of other ethnic groups in Nigeria. Also, having daughters only (no sons) was associated with higher odds of unrealized fertility, after controlling for other important covariates. The findings suggest that cultural norms and pronatalism significantly influence the fertility desires of women in Nigeria, even at the end of their reproductive lifespan.

This paper argues that son preference resulted in gender-based discriminatory practices that unduly increased mortality rates for females at birth and throughout infancy and childhood in nineteenth- and early-twentieth-century Greece. The relative numbers of boys and girls at birth was extremely high and under-registration of females cannot on its own explain this result. The infanticide and/or mortal neglect of infant girls was therefore more common than previously acknowledged. Likewise, sex ratios increased as children grew older, thus suggesting that parents continued to treat boys and girls differently throughout childhood. A large body of qualitative evidence (contemporary accounts, folklore traditions, feminist newspapers, and anthropological studies) further supports the conclusion that girls were neglected due to their inferior status in society.

In this paper, we use linked census data from England and Wales to investigate whether having a large number of siblings leads to lower educational attainment. There is a large literature suggesting that with large sibship size, parental resources will be diluted and this, in turn, will lead to lower educational attainment. Using twin births and the sex composition of the sibling group as instrumental variables, we find that the evidence of a family size effect on educational attainment is rather uncertain. Similar results are obtained when we use occupational attainment as the dependent variable. We also demonstrate the confounding of birth order and family size effects, and show that an adjusted birth order index proposed by Booth and Kee provides an effective solution to this estimation problem.

This paper explores gene–environment interactions—interactions between family environments and children’s genetic predispositions—in determining educational attainment. The central question is whether poor childhood family environments reduce children’s ability to leverage their genetic gifts to achieve high levels of educational attainment—are there important ‘bottlenecks’ for poor children? The multigenerational information and genetic data contained in the United States’ Health and Retirement Study are used to separate two mechanisms for intergenerational transmission of socio-economic status: genetic endowments and family environments. Using parental in utero exposure to the 1918–19 influenza pandemic as a source of quasi-experimental variation in family environments (that did not affect children’s genetic endowments), I estimate interactions between parental investments and children’s genetic potential. The main finding suggests that girls with high genetic potential whose fathers were exposed to influenza face reduced educational attainments—a gene–environment interaction—but there is no similar effect for boys.

This paper examines the long-term effects of birth cohort size on life outcomes. Using administrative data from Singapore, we study the outcomes of large birth cohorts created by the Chinese superstitious practice of zodiac birth timing, where parents prefer to give birth in the year of the Dragon. This practice is followed exclusively by the Chinese majority, with no similar patterns detected among non-Chinese minorities, allowing us to differentiate cohort size effects from confounding year-of-birth effects. Despite government efforts to increase public educational resources for these cohorts, Chinese Dragons earn lower incomes and are less likely to gain admission to national universities. There is also evidence of negative externalities on non-practising populations who happen to enter the labour market at the same time as Chinese Dragons. Our analysis suggests that the adverse life outcomes are not due to selection, but rather reflect the aggregate resource implications of birth cohort size.Supplementary material is available for this article at: https://doi.org/10.1080/00324728.2020.1864458.

The presence, number, sex, and age composition of children within families can have important influences on couples' marital outcomes. Children are valued across settings, but their value in settings where there is an absence of formalized social security is distinctive. This paper explores the influences of childlessness, and different number, age, and sex compositions of children, on the odds of marital dissolution among couples in rural Nepal. Results reveal that childless couples face significantly higher odds of dissolution than couples with at least one child, and each additional child-up to three children-reduces couples' odds of dissolution. Furthermore, having a child aged under two reduces couples' odds of marital dissolution, but interactions reveal that this age effect only holds at parity one. Surprisingly, despite a history of son preference in this setting, there is no evidence that children's within-parity sex composition is associated with the odds of marital dissolution.

The present paper is part of a larger analysis of data collected in the summer of 1970 in the city of Cairo. The present analysis is based on a sub- sample of 569 households. The main objectives of the paper are: [(1)] to establish the existence of a difference between actual fertility and ideal fertility; [(2)] to show that the difference is related to some socio-economic and modernization variables; and [(3)] that differences in actual and ideal fertility in different social groups are similar and [(4)] that these differences can be explained to a substantial extent by differences in the use and the use-effectiveness of contraception. Respondents were asked how many children they wished to have themselves and also how many children they would want or consider ideal for Egyptians generally. Husbands also expressed their preferences. This is what Stycos calls a fertility belief system the sum total of consciously held beliefs and attitudes common to a group which have explicit preference to fertility behaviour. (excerpt)

Classic demographic theories conceptualize desired family size as a fixed goal that guides fertility intentions over the childbearing years. However, a growing body of research shows that fertility plans, even nominally long-term plans for completed childbearing, change in response to short-term conditions. Because of data limitations, much of this research has focused on low-fertility contexts, but short-term conditions are likely to be even more important in high-fertility contexts. This paper uses three waves of survey data collected in rural Mozambique to study predictors of the desire to stop childbearing in a context of relatively high fertility and high individual and social instability. We use fixed effects models to assess how women's desires to stop childbearing are shaped by demographic factors, household economic conditions, and health status, controlling for constant individual characteristics. Results provide evidence that fertility desires both reflect stable underlying goals and evolve in response to individual and social circumstances.

This paper presents an examination of how religio-ethnic identity, individual religiosity, and family members’ religiosity are related to preferred family size in Nepal. Analyses of survey data from the Chitwan Valley Family Study show that socioeconomic characteristics and individual experiences can suppress, as well as largely account for, religio-ethnic differences in fertility preferences. These religio-ethnic differentials are associated with variance in particularized religious theologies or general value orientations (like son preference) across groups. In addition, individual and family religiosity are both positively associated with preferred family size, seemingly because of their association with religious beliefs that are likely to shape fertility strategies. These findings suggest improvements in how we conceptualize and empirically measure supra-individual religious influence in a variety of settings and for a range of demographically interesting outcomes.

This paper offers an empirical and analytic foundation for regarding period life expectancy as a lagged indicator of the experience of real cohorts in populations experiencing steady improvement in mortality. We find that current period life expectancy in the industrialized world applies to cohorts born some 40-50 years ago. Lags track an average age at which future years of life are being gained, in a sense that we make precise. Our findings augment Ryder's classic results on period-cohort translation.

It is well established that young people whose parents divorced or experienced marital breakdown during their childhood are likely to enter into first partnerships and into parenthood earlier than those whose parents remained married. In this paper using data from the British National Sexual Attitudes and Lifestyles Survey we examine how far the timing of first coitus plays a role in the genesis of this demographic behaviour for children of divorced parents. Other factors including the timing of menarche attitudes to sexual activity degree of parental strictness and religiosity were also examined. In general these factors had little explanatory power. The analysis showed that earlier sexual activity for men and women from disrupted families is an important proximate determinant of their earlier entry into partnership and parenthood compared with those brought up with both natural parents. (EXCERPT)

The hypothesis that minority status creates social tensions that affect fertility behaviour attracted much attention during the late 1960s and 1970s, but then disappeared after 1980. This sudden exit was due to a combination of methodological difficulties in distilling the independent effects of minority status from other socio-economic factors, weaknesses or ambiguities in the empirical record, and other difficulties. This paper examines a natural experiment that serendipitously by-passes more of these problems than has been heretofore possible – the attempt by Chinese in Malaysia to time births into the auspicious Year of the Dragon. A multivariate model shows that this unique fertility behaviour was more common in Malaysian districts with smaller proportions of Chinese, which suggests that minority status can directly affect ethnic identity. The results also highlight a paradoxical solution to a grander problem facing socio-demographic theory. Before we can posit that culture or values play an independ...

Age-at-marriage estimates from family reconstitutions may be biased downward when they are based only on marriages of people who continue to live in their parish of birth, because when the probability of migrating rises with age, younger people are selected in preference to older ones. Micro-simulations show that the bias can have dramatic effects. In this paper French-Canadian data are used to investigate the importance of the bias and to verify empirically the micro-simulation results. Although a high proportion of people moved between birth and marriage, the bias had virtually no effect, given the specific characteristics of the migrations. If one cannot avoid discussing the timing of migration before marriage, when measuring age at first marriage using only data on “stayers”, it is just possible that in most settings, it is the same for those who lived in their parish of birth, and those who had moved.

In their attempts to distinguish empirically between the innovation/diffusion and adaptation views of fertility transition, researchers have pointed out that evidence of fertility control practised by a significant proportion of women in pre-transition populations would render claims that fertility fell as a result of innovative behaviour less convincing. This paper uses simulation techniques to evaluate the ability of two indirect measures of fertility control, Coale and Trussell's model (M & m) and Cohort Parity Analysis (CPA), to identify the presence or absence of fertility controllers, as well as to detect changes in the extent of control. We conclude that neither M & m nor CPA can be relied on to identify accurately a minority of controllers in a population of interest. These findings suggest the need for a reassessment of some of the evidence cited in the debate over alternative theories of fertility decline.

Many studies have suggested that unmarried adolescent childbearing is becoming a social problem in many countries of sub-Saharan Africa, because it tends to lead to school drop-outs, illegal abortions, and child abandonment. To date, the motivations for adolescent childbearing remain poorly understood. One point of view is that unmarried adolescent childbearing results from a breakdown of social controls by the elders over young people. Others have argued that adolescent childbearing is a form of rational adaptation; a means to achieve a specific goal. For example, girls may choose to become pregnant if they believe that a pregnancy will lead to marriage. In this paper adolescent sexual activity and premarital childbearing in seven sub-Saharan African countries are examined with data from Demographic and Health Surveys. In a first section, the impact of socio-economic indicators on adolescent sexual and reproductive behaviour is examined; a subsequent section is focused on the motivation for different typ...

Despite previous research on the relationship between husband's or wife's level of educational attainment and childbearing and child spacing, relatively few data exist on couples' combined educational attainment which compares whites and non-whites. Further, to date a systematic exploration of available information contained on the 1/1,000 sample of the United States population in 1960 has not been undertaken. This paper utilizes these data and investigates the time intervals between marriage and first birth and between subsequent events to determine what relationships exist between parity and child spacing for white and non-white couples by level of educational attainment.

Summary Previous research on the relationship between extended family residence and fertility has produced conflicting findings. In the present paper, we avoid a major shortcoming of past work by focusing on residence and fertility at a given stage of the life-cycle, i.e. the stage following first marriage. Results show that residence with husband's parents reduces age at marriage. Residence with wife's parents shows no such consistent effect. No evidence was found to support the claim that extended family residence consistently affects the length of the interval between marriage and the first birth. These findings are consistent across four cultural/ethnic groups.

Whether a couple remain married or divorce has repeatedly been shown to be of importance for the marital stability of their children. This paper addresses the related question of whether the intergenerational transmission of divorce is contingent on the age at which parents divorced and the sex of the spouse who experienced the parents’ divorce. Using a population-wide data-set on Norwegian first marriages followed from 1980 to 2003, we find that the intergenerational transmission hypothesis holds also for Norway, that this relationship is stronger for women than for men, and that there is a negative age gradient in the transmission effect for women. The experience of multiple family transitions, such as a parent's remarriage or a second divorce, does not affect couples’ divorce risk.

This paper attempts to disentangle simultaneous demographic effects on divorce probabilities by means of age-period-cohort-type models. A multi-dimensional analysis of divorce probabilities in Finland between 1948 and 1984 is presented by period, marriage cohort, and duration, and for the year 1984 by age, age at marriage, and duration. Effects of order of marriage, number of children, and age of youngest child are also studied. Finland is one of the few countries in which such data are available from a population register. For the changes between 1948 and 1984, period effects turn out to be much more important for the increase in divorce than cohort effects. As regards period analysis for 1984, a quite surprising pattern appears: neither a specific duration of marriage (usually risk is highest at durations of between four and six years), nor a young age at marriage present the major risk factors, but young age itself. If this pattern were also to hold for other populations, it suggests the need for a maj...

Japanese household structure has changed dramatically over the last two decades, especially with regard to multi-generational co-residence. In this paper, we use logit analysis to investigate the extent to which married Japanese men and women aged 30 to 59 live with their parents and, in particular, how socio-economic and demographic characteristics are associated with co-residence. For men, being the eldest child, being in a lower-status occupation, living in a small town or rural area, being in an arranged marriage, and having a parent without a spouse are all positively associated with co-residence. For women, only demographic variables matter – being the eldest child, having a husband who is not the eldest child, and having a parent without a spouse, lead to a higher probability of co-residence with own parents. For those middle-aged Japanese who are not co-residing with their parents, we analyse the frequency of seeing and telephoning their parents and find that the distance between the residences of...

Arabs in Israel are a heterogeneous but largely underprivileged minority with a history of disadvantage in several domains, including education and employment. In this paper, we document changes in their attainment of various educational levels across cohorts born from the mid-1920s to the 1970s. We make comparisons among different Arab religious groups, between men and women, and between Arabs and the majority Jewish populations in Israel. We find that over consecutive birth cohorts, substantial ethnic differences in educational attainment have narrowed at the lower levels of schooling, but have increased at higher levels. Moreover, the results indicate that the disadvantage of Muslim Arabs in terms of entry into and completion of high school can be accounted for only partially by differences in the social status of their parents and characteristics of their neighbourhoods. The findings suggest that long-term historical differences among groups and discriminatory practices towards Arabs are important factors in explanations of disparities in educational attainment.

This paper examines excess mortality following spousal bereavement by time since bereavement, sex, age, and education. The main hypothesis challenged is that higher education buffers the harmful effects of spousal loss. Using a log-rate model, death-rate ratios (widowed/married) are estimated for 49,849 and 126,746 Belgian widowers and widows and an equal number of non-bereaved controls matched to the bereaved on their socio-demographic characteristics. The hypothesis that the more educated suffer less excess mortality is not supported. Although higher educational levels are associated with lower mortality in general, they do not alleviate the effects of bereavement. On the contrary, in the period immediately following spousal loss, the more highly educated seem to have more, rather than less, excess mortality. Three possible arguments are suggested to account for this: education-related differences in the partner-relationship, structural differences in the availability of appropriate social support, and cultural differences in potential support networks.

Summary Does the minority group status of blacks exert an influence on their fertility? This paper expands the theory of minority group status by distinguishing the types of effects it simultaneously exerts on black fertility. In addition, this study suggests a conceptual and empirical innovation by considering variations in structural milieu, as well as the characteristics of individuals (status indicators) in their effects on fertility. Data from the 1970 Census Public Use Sample are used in this analysis. The analysis supports the conceptualization of different types of minority group status effects and underscores their relevance for understanding the current fertility differential between blacks and whites. But when the black population has become assimilated, it is suggested that the two groups may be expected to exhibit similar fertility.

In this paper information about cohorts of young women in the National Longitudinal Survey of Work Experience is used to examine the extent to which women maintain a continuity of work attachment during their early years of childbearing the years when traditionally they were most likely to withdraw from the workforce. It has been shown in earlier studies of labor market experience how the traditional pattern has been eroding and how large numbers of young women are now choosing to retain close ties to the labor market during the months just before and even just after childbearing. The hypothesis was put forward that the work activity of a substantial proportion of women at this critical point in their life cycle when they had their 1st child was a major indicator of social change and symptomatic of a substantial and continuing attachment to work. These hypotheses are examined by focusing on the early years of childbearing e.g. the 5 to 10 years following the birth of a 1st child. This is the period during which women have young children to care for and when traditionally laborforce participation was lowest. The strength of the link between early and later laborforce participation and the degree to which this link is mediated by intervening fertility and other economic considerations are analyzed. The data support the suggestion that strong attachment to the workforce as manifested by employment both before and after the 1st birth is linked with a greater likelihood of lifetime commitment to labor market activity. Conversely weak early attachment as manifested by nonemployment before and after the 1st birth presages quite limited subsequent work activity. Higher educational achievement is associated with higher laborforce participation during the early years of childbearing. The positive association between schooling and later work attachment persists even when employment behavior around the period of 1st birth is controlled. The results indicate that women who maintain closer ties to the workforce immediately before and after their 1st birth are also more likely to be employed in 1978--between 5 and 10 years after their 1st birth--independently of intervening fertility events and other labor supply factors considered to be important predictors of work. The notion that work and fertility are increasingly becoming complementary activities for American women is supported by this data.

This paper examines the relationship between the number of partnerships ever engaged in and fertility, as measured by the average number of live births. It was found that the larger the number of partnerships in which a woman had been engaged the higher is her fertility. This relationship between partnerships and fertility remains even when such variables as present age, age at first partnership, age at first pregnancy, time lost between unions, time spent in partnerships, time since entry into the first partnership, type of sexual union at first pregnancy, present type of sexual union, and current use or non-use of contraceptives are controlled by cross tabulation. Correlation analysis also bears out the positive relationship between partnerships and fertility. The data for this study came from a sample survey of 4,199 women of lower, and lower middle, socio-economic status who were interviewed in 1971 on the island of Barbados. The authors have confidence in the reliability and validity of their data and hence in their findings and conclusions. The authors believe that their findings contradict the previously established positive relationship between patterns of stability of sexual unions and fertility in English-speaking Caribbean societies. They conclude that the relationship was either not rigorously examined in the past or else has undergone changes as these societies modernize economically and socially.

This paper discusses the suitability of data on the fertility of polygamous marriages for drawing inferences on the effect of coital frequency on fertility. The author concludes that it may be possible to utilise these data, provided polygamous husbands distribute their sexual activity among all their wives, so that coital frequency for a polygamous wife is lower than that of a monogamous one. Polygamous Arab Beduin may be supposed to have intercourse regularly with all their wives. The author shows that childlessness is higher among first and second polygamous wives than among monogamous ones, and that the average number of children per fertile woman is lower. The higher incidence of childlessness may be due to response errors, or may demonstrate that childlessness is an incentive to polygamy. But the smaller average number of children per fertile woman shows a real differential. It is also shown that although the number of children born to polygamous women is smaller than that of monogamous wom...

The paper shows that persons who have passed matriculation differ from the rest of the population in marital status and the number of live births. Marriage frequency among male students is higher, and that among female students lower, than that for the urban population of the same age. The proportion of childless marriages is smaller among male students than among the rest of the population. The trend of fertility has been different for students as compared with other males of the same age. Fertility among students (of 1910 and 1920) has risen and among the rest of the population of the same age it has fallen. The most striking difference between the students and the rest of the population is to be found in the fact that for the students there is a positive and for the rest of the (urban) population a negative correlation between income and number of children. Finally, the data suggest that among Swedish students there may be a slight positive correlation between intelligence and number of children.

The author comments on a paper by S. Mitra in which an alternative formula for estimating the expectation of life at advanced ages is proposed. A reply by Mitra (pp. 511-2) is included. (ANNOTATION)

Summary The paper examines hypotheses that certain aspects of status of married women such as (i) decision-making power; (ii) employment status and (iii) educational status, are positively associated with use of contraception and inversely related to fertility performance. The study is based on 1,130 women of reproductive age (15-49) who are currently married and living with their husbands and reported to be fecund. The data are drawn from a cross-section of working and non-working women of Dacca City. The hypothesis that each of the above status variables is related to fertility behaviour (measured as current use of contraception and number of children ever-born) is confirmed, with the sole exception of the relationship between female employment status and fertility behaviour. Female participation in the labour force has little or no effect on use of contraception, particularly among those who belong to higher education and income groups. However, in the lower education and income groups, fertility and u...

In this paper are formulated some convenient summary measures of fertility patterns. These measures, which are based on the Gompertz function, are total lifetime fertility, median age of mothers at childbirth, and inter-quartile range of age of mothers at childbirth. Estimates of the parameters of Gompertz function, based on Canadian data, are used to derive, for each of the summary measures, values which reflect historical fertility experience, and thus give an impression about the range of realistic values for these measures. A simple model of demographic activity which includes the Gompertz function is also considered, and this model is used in computer simulation experiments to determine the macro-demographic effects of changes in each of the three summary measures.

Summary This paper describes the results obtained in administering a modified Terman intelligence test to 327 Greek children aged from 7 to 12 years. A negative correlation between intelligence and family size was obtained. The results are compared with those obtained in similar inquiries in Britain and the U.S.A.

In this paper data relating to men born in 1924 in the two southernmost counties of Sweden, and called up for military service in 1944 are analyzed. The population registers yield certain demographic and social information about these men, and this may be related to their performance in an intelligence test administered when they were called up. The association between test scores and level of schooling on one hand, and such variables as nuptiality, age at marriage, number of sibs, marital fertility, the incidence of pre-nuptial conceptions and occupational class is discussed, and an estimate of the influence of differential fertility on the trend of intelligence is given.

Summary This paper analyses the replies to certain questions on ideal family size, family planning and the limitation of offspring and attitudes towards the use of contraceptives of 1,022 white married women recently interviewed in a Johannesburg fertility survey. Replies to questions on the above topics are correlated with certain sociological variables such as home language, religion, educational status, family income and occupation. The application of these controls to the sample data revealed some interesting differences in outlook with regard to family size, family planning and the use of contraceptives. Home language and religious affiliation were found to be amongst the most important variables. Generally speaking, in spite of some significant differences in fertility attitudes between certain groups composing the sample population, there appeared to be a good deal of uniformity with regard to ideal family size, family planning and the use of contraceptives.

The paper summarizes the procedure usually employed by Enke, Meier and others to estimate the benefit-cost ratio of a prevented birth. Some possible deficiencies in the formulation, the possible lack of relevance of the resulting computations, are considered. For example, since the benefit-cost ratios are exceptionally high they would imply unusually high rates of investment for family planning. The results would also apply for the birth prevention of not only high parity births, but also for first and second children. Some arguments are presented which suggest the possibility that the income distribution might be worsened as a consequence of the application of a family planning programme based on these principles - especially those which employ subsidies to induce the practice of family limitation. In addition it is also argued that the average economic quality of the population may be lower than otherwise as a consequence of such programmes, and that the consequences of such events are not taken into account in the usual formulation. Also the usual estimates of costs of such programmes are questioned since the relation between acceptances and births prevented are unknown given the lack of knowledge about the substitution between the proposed methods of family limitation and other means of population control. Finally, we present a model based on reasonable but different assumptions than the formulation popularized by Enke and others, and show that on the basis of this model it is possible to obtain results which are the exact opposite of the Enke model. Also it is argued that the model presented is much more sensitive to actual data than the usual formulation.