Ester Lucia Rizzi

The seasonality of conception.

Individual data on menstrual cycles of noncontracepting women living in Western countries were used in order to verify whether the biological seasonality of conception persists after sexual behavior is controlled for. Episodes of intercourse were recorded daily, and the time of ovulation was detected by a marker. We find that the seasonality of conception changes with woman’s age and frequency of episodes of sexual intercourse. In particular, for women aged 27–31 having only one act of intercourse during the six most fertile days of the menstrual cycle, the seasonality of fecundability is stronger. In this age group in the Northern Hemisphere, if seasonality of acts of sexual intercourse is controlled, the monthly distribution of probability of conception is bimodal, with two maxima (September and January) and two minima (December and March). When unobserved characteristics of the couples are considered, this seasonal pattern of conception persists.

The science network in Italian population research : An analysis according to the social network perspective

The scientific community organises its relationships into network patterns, where the nodes are individuals (scientists) and the links are acquaintance and common work, usually presented at workshops and conferences and/or published in books and scientific journals. A references review on Population Studies by Italian scientists is delivered every two years by the Demography Section of the Italian Statistical Society; the review is exhaustive for academic demographers. In this paper, the properties of the demographers’ network in 1998–1999 are evaluated, with the aim of identifying factors which may influence collaborative relations among actors. The probability of cooperation between couples (dyads) of demographers is modelled, conditionally on observed characteristics of the dyad (sex, academic position, university affiliation). Main results suggest that “closeness”, defined in a wider sense and not simply as geographical proximity, plays a major role in determining actors’ relationships.

Age effect : results from a detailed prospective study on daily fecundability

BACKGROUND Demographers, epidemiologists and clinicians have long been interested in the estimation of age-specific fecundability. With the progressive postponement of age at family formation in Western countries, this topic has recently become the focus of renewed attention. METHODS In order to correctly estimate the effect of biological ageing on fecundability it is crucial to collect detailed information through a rigorous study design and to apply suitable models for analysing time to pregnancy data. In this article we discuss some methodological problems concerning the study of fecundability and its dependence on biological ageing. We also present the Multinational Study in Daily Fecundability which has produced a very rich database with detailed behavioural and physiological information prospectively collected on every cycle. Finally, we review some results on age effects obtained from these data. RESULTS Our findings show that the decline in fecundability from age 28 to age 33 is not statistically significant and very modest. CONCLUSION The results presented here do not appear to be particularly alarming with regard to the postponement of conception of the first child from age 28 to 33. This postponement could however lead to attempts to conceive a second child after age 35, when fecundability starts to decrease rapidly and when the risk of genetic disorders increases.

How Do Life Course Events Affect Paid and Unpaid Work of Italian Couples

The paper analyzes the impact of life course events, and in particular of parenthood, on the paid and unpaid working activity of dual-earner couples in Italy. To this purpose, we use the panel dataset provided by the 2003--2007 Istat Multipurpose Survey. To correct misspecification due to unobserved variables, we adopt a difference-in-differences specification of simultaneous equations of market and domestic work supply. Our results show that the negative effect of transition to parenthood on female paid work supply is stronger than the positive effect of wages.

Parenthood and labour division in Italian two-earner couples

Purpose Lack of robustness of findings characterizes the empirical studies about the effect of the transition to parenthood on partners’ labour division. In this analysis, the purpose of this paper is to solve these problems through the conjoint use of methodological instruments of regression analysis, allowing the authors to correct for the effects of omitted variables. Design/methodology/approach A correction method is here applied to a longitudinal simultaneous equation model. In particular, the authors impose specific constraints on the covariances of the error terms of the longitudinal simultaneous equations of the paid and domestic work of both partners. For the empirical analysis, use is made of the Italian National Institute of Statistics Multipurpose Panel Survey in the years 2003 and 2007 to select a survey sample of dual-earner Italian couples. Findings The authors found that the negative influence of motherhood on the Italian women’s paid work supply is stronger than the positive effect of wage. The authors found that having a child (whatever the order) decreases a woman’s paid work hours by 17 hours a week, while woman’s domestic work increases by 20 hours a week as the effect of the birth of the first child. Originality/value Compared to Fixed Effect or Change-Score models suggested for longitudinal studies the Seemingly Unrelated Regression Equations-Difference-in-Differences procedure let us obtain estimations also for the effect of time-invariant variables. In addition, the methodological approach allows us to correct estimates for the common effects that latent variables exert simultaneously (e.g. the bargaining process) on paid and unpaid work equations of both partners.