Kevin Lewis

December 25, 2010

On the Relation Between Fertility, Natality, and Nuptiality

Alexia Prskawetz, Marija Mamolo & and Henriette Engelhardt
European Sociological Review, December 2010, Pages 675-689

Recent studies of fertility in Europe indicate a changing cross-country correlation between total fertility and fertility-related behaviour. Fertility now tends to be lowest in countries that are traditional, catholic, and family-oriented, while it is highest in countries with high divorce rates, high rates of cohabitation, and high levels of extra-marital births. In this article we provide support to the argument that the change in the cross-country correlation between fertility and fertility-related behaviour may indicate a change in social context of this fertility-related behaviour that has helped to uncover cross-country differences in social norms, culture, and institutional settings. We apply pooled time series analysis and show that time and country heterogeneity in the association between fertility and fertility-related behaviour can explain the change in the cross-country correlation. Our results also indicate that further postponement of marriage and motherhood leads to less pronounced declines in fertility.


Intranasal oxytocin increases fathers' observed responsiveness during play with their children: A double-blind within-subject experiment

Fabienne Naber et al.
Psychoneuroendocrinology, November 2010, Pages 1583-1586

Recent correlational studies showed that oxytocin is associated with parenting style in humans as in other mammals. Here the first double-blind, placebo-controlled, within-subject experiment with intranasal oxytocin administration is presented. Subjects were 17 fathers with their toddler, observed in two play sessions of 15 min each with an intervening period of 1 week. In the oxytocin condition fathers were more stimulating of their child's exploration than in the placebo condition, and they tended to show less hostility. Parent training experiments might be combined with intranasal oxytocin administration to test differential and cumulative effects of traditional, interaction-focused versus pharmaceutical treatments.


The plasticity of human maternal brain: Longitudinal changes in brain anatomy during the early postpartum period

Pilyoung Kim, James Leckman, Linda Mayes, Ruth Feldman, Xin Wang & James Swain
Behavioral Neuroscience, October 2010, Pages 695-700

Animal studies suggest that structural changes occur in the maternal brain during the early postpartum period in regions such as the hypothalamus, amygdala, parietal lobe, and prefrontal cortex and such changes are related to the expression of maternal behaviors. In an attempt to explore this in humans, we conducted a prospective longitudinal study to examine gray matter changes using voxel-based morphometry on high resolution magnetic resonance images of mothers' brains at two time points: 2-4 weeks postpartum and 3-4 months postpartum. Comparing gray matter volumes across these two time points, we found increases in gray matter volume of the prefrontal cortex, parietal lobes, and midbrain areas. Increased gray matter volume in the midbrain including the hypothalamus, substantia nigra, and amygdala was associated with maternal positive perception of her baby. These results suggest that the first months of motherhood in humans are accompanied by structural changes in brain regions implicated in maternal motivation and behaviors.


Aftershocks: The Impact of Clinic Violence on Abortion Services

Mireille Jacobson & Heather Royer
American Economic Journal: Applied Economics, forthcoming

Between 1973 and 2003, abortion providers in the United States were the targets of over 300 acts of extreme violence, including arson, bombings, murders and butyric acid attacks. After a period of decline, abortion clinic violence is on the rise again. The recent murder of Dr. George Tiller has brought attention back to the role of extreme violence in the anti-abortion movement. Using unique data on attacks and on abortions, abortion providers, and births, we examine how anti-abortion violence has affected providers' decisions to perform abortions and women's decisions about whether and where to terminate a pregnancy. We find that clinic violence reduces both abortion providers and abortions in the areas where the violence occurs. Once travel is taken into account, however, the overall effect of the violence is much smaller. On net, roughly 90 percent of the fall in abortions in targeted areas is balanced by a rise in abortions in nearby areas. Thus, the main consequence of this violence is a displacement rather than an elimination of abortions, a presumed goal of this terrorism.


Intercountry Versus Transracial Adoption: Analysis of Adoptive Parents' Motivations and Preferences in Adoption

Yuanting Zhang & Gary Lee
Journal of Family Issues, January 2011, Pages 75-98

The United States is one of the major baby-receiving countries in the world. Relatively little research has focused on why there is such a high demand for intercountry adoption. Using in-depth qualitative interviews with adoptive parents, the authors explored the reasons why Americans prefer to adopt foreign-born children instead of adopting minority children domestically. Other than infertility reasons, concerns about domestic adoption, and the uneven domestic supply and demand of "desirable" children, the authors' findings suggested that there was a perception that American children available for adoption presented difficult problems whereas foreign children presented interesting challenges. The "problems" inherent in children from American foster care were confounded with race differences. Studying adoption motivations will not only help us better understand the domestic adoption situation, especially why so many Black children are left behind in foster care, it may also reveal important insights into current race relations and distances between groups in the United States.


Do Siblings' Fertility Decisions Influence Each Other?

Torkild Hovde Lyngstad & Alexia Prskawetz
Demography, November 2010, Pages 923-934

Individuals' fertility decisions are shaped not only by their own characteristics and life course paths but also by social interaction with others. However, in practice, it is difficult to disentangle the role of social interaction from other factors, such as individual and family background variables. We measure social interaction through the cross-sibling influences on fertility. Continuous-time hazard models are estimated separately for women's first and second births. In addition to individual socioeconomic variables, demographic variables, and an unobserved factor specific to each sibling pair, siblings' birth events and their timing enter as time-varying covariates. We use data from longitudinal population-wide Norwegian administrative registers. The data cover more than 110,000 sibling pairs and include the siblings' fertility, education, income, and marital histories. Our results indicate that cross-sibling influences are relatively strong for the respondents' first births but weak for the second parity transition.


Effects of oxytocin on recollections of maternal care and closeness

Jennifer Bartz et al.
Proceedings of the National Academy of Sciences, 14 December 2010, Pages 21371-21375

Although the infant-caregiver attachment bond is critical to survival, little is known about the biological mechanisms supporting attachment representations in humans. Oxytocin plays a key role in attachment bond formation and maintenance in animals and thus could be expected to affect attachment representations in humans. To investigate this possibility, we administered 24 IU intranasal oxytocin to healthy male adults in a double-blind, placebo-controlled, crossover designed study and then assessed memories of childhood maternal care and closeness - two features of the attachment bond. We found that the effects of oxytocin were moderated by the attachment representations people possess, with less anxiously attached individuals remembering their mother as more caring and close after oxytocin (vs. placebo) but more anxiously attached individuals remembering their mother as less caring and close after oxytocin (vs. placebo). These data contrast with the popular notion that oxytocin has broad positive effects on social perception and are more consistent with the animal literature, which emphasizes oxytocin's role in encoding social memories and linking those memories to the reward value of the social stimulus.


Factors influencing physicians' advice about female sterilization in USA: A national survey

R.E. Lawrence, K.A. Rasinski, J.D. Yoon & F.A. Curlin
Human Reproduction, January 2011, Pages 106-111

Background: Tubal ligation can be a controversial method of birth control, depending on the patient's circumstances and the physician's beliefs.

Methods: In a national survey of 1800 US obstetrician-gynecologist (Ob/Gyn) physicians, we examined how patients' and physicians' characteristics influence Ob/Gyns' advice about, and provision of, tubal ligation. Physicians were presented with a vignette in which a patient requests tubal ligation. The patient's age, gravida/parity and her husband's agreement/disagreement were varied in a factorial experiment. Criterion variables were whether physicians would discourage tubal ligation, and whether physicians would provide the surgery.

Results: The response rate was 66% (1154/1760). Most Ob/Gyns (98%) would help the patient to obtain tubal ligation, although 9-70% would attempt to dissuade her, depending on her characteristics. Forty-five percent of physicians would discourage a G2P1 (gravida/parity) woman, while 29% would discourage a G4P3 woman. Most physicians (59%) would discourage a 26-year-old whose husband disagreed, while 32% would discourage a 26-year-old whose husband agreed. For a 36-year-old patient, 47% would discourage her if her husband disagreed, while only 10% would discourage her if her husband agreed. Physicians' sex had no significant effect on advice about tubal ligation.

Conclusions: Regarding patients who seek surgical sterilization, physicians' advice varies based on patient age, parity and spousal agreement but almost all Ob/Gyns are willing to provide or help patients obtain surgical sterilization if asked. An important limitation of the study is that a brief vignette, while useful for statistical analysis, is a rough approximation of an actual clinical encounter.


Season of birth and subsequent body size: The potential role of prenatal vitamin D

Marta Krenz-Niedbała, Elżbieta Puch & Krzysztof Kościński
American Journal of Human Biology, forthcoming

Objectives: The relationship between season of birth and various physical and psychological outcomes was reported in many studies, although the underlying mechanism still remains unrecognized. The aim of this study was to explore the season-of-birth effect on body size in the sample of 1,148 eight-year-old Polish urban children and propose the mechanism responsible for this effect.

Methods: The children were examined three times at their birthdays and at two cross-sectional surveys. Effects of the season of birth were checked by fitting the cosine function to empirical values and by comparison between two groups born in different periods of the year.

Results: Data gathered at three examinations led to the same results: season-of-birth effect occurred only in boys and only in those relatively shortly breastfed and/or descended from the families of low-socioeconomic status. Specifically, the individuals born in October-April were taller (by 2-3 cm), heavier (by 2-3 kg), and fatter than those born in May-September.

Conclusions: The following explanatory mechanism has been formulated: insolation in Poland is minimal in November-February (winter period), and so ultraviolet absorption and vitamin D production is then the lowest. Vitamin D regulates embryo's cellular differentiation, and its deficiency triggers permanent developmental changes. Therefore, individuals conceived in autumn (i) are at the greatest risk of early vitamin D deficiency, (ii) are born in summer, and (iii) are relatively small in their further lives. The contribution of low-socioeconomic status, short breastfeeding, and being a male to the occurrence of the season-of-birth effect is also discussed.


Maternal and paternal plasma, salivary, and urinary oxytocin and parent-infant synchrony: Considering stress and affiliation components of human bonding

Ruth Feldman, Ilanit Gordon & Orna Zagoory-Sharon
Developmental Science, forthcoming

Studies in mammals have implicated the neuropeptide oxytocin (OT) in processes of bond formation and stress modulation, yet the involvement of OT in human bonding throughout life remains poorly understood. We assessed OT in the plasma, saliva, and urine of 112 mothers and fathers interacting with their 4-6-month-old infants. Parent-infant interactions were micro-coded for parent and child's social behaviors and for the temporal coordination of their socio-affective cues. Parents were interviewed regarding their attachment to the infant and reported on bonding to own parents, romantic attachment, and parenting stress. Results indicated that OT in plasma (pOT) and saliva (sOT) were inter-related and were unrelated to OT in urine (uOT). pOT and sOT in mothers and fathers were associated with parent and child's social engagement, affect synchrony, and positive communicative sequences between parent and child. uOT was related to moments of interactive stress among mothers only, indexed by the co-occurrence of infant negative engagement and mother re-engagement attempts. pOT and sOT were associated with mothers' and fathers' attachment relationships throughout life: to own parents, partner, and infant, whereas uOT correlated with relationship anxiety and parenting stress among mothers only. Similar to other mammals, OT is involved in human attachment and contingent parenting. The dual role of OT in stress and affiliation underscores its complex involvement in processes of social bonding throughout life.


Hockey success and birth date: The relative age effect revisited

Joseph Nolan & Grace Howell
International Review for the Sociology of Sport, December 2010, Pages 507-512

In a replication of studies by Barnsley et al. (1985), and Grondin et al. (1984) the authors gathered birthdates of players in the National Hockey League (NHL), Western Hockey League (WHL), Ontario Hockey League (OHL), and Quebec Major Junior Hockey League (QMJHL). The players were categorized according to month of birth. Additionally, the players were categorized by country of birth, reflecting the changes in professional hockey over the period since the original studies. The results indicate that despite the globalization of hockey and changes in minor hockey, relative age effect, that is, a strong linear relationship between the month of birth (from January to December) and the proportion of players in the leagues studied, still exists.


A Closer Look at the Relative Age Effect in the National Hockey League

Vittorio Addona & Philip Yates
Journal of Quantitative Analysis in Sports, October 2010

At young ages, a few extra months of development can make a big difference in size, strength, and athletic ability. A child who turns 5 years old in January will be nearly 20% older by the time a child born in December has their 5th birthday. In many sports, including hockey, children born in the early months of the calendar year get noticed by their coaches because of the superiority they demonstrate due to their age advantage. As a result, boys born early in the year are more likely to reach the professional ranks of the National Hockey League (NHL). The phenomenon just described has been labeled the relative age effect (RAE). Previous work studying the RAE in the NHL has focused on individual NHL seasons, often encompassing many of the same players across multiple seasons. We investigate the RAE using complete data on every player who has ever played in the NHL. We focus the majority of our analysis on Canadian born players and examine the RAE across hockey position and hall-of-fame status. For the first time, we provide strong evidence of when the RAE began to manifest itself in Canada. Our change point analysis indicates that the RAE began for players born since 1951. Finally, we make a case for what initiated this change in the way young hockey players develop, particularly in Canada, which produced over 90% of NHL players at that time.

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