The fall of internal migration

It is costly to move, and those costs vary by culture and economic circumstances. International migration is of course hampered by immigrations laws and cultural barriers. But in most countries, internal migration is free and only restrained by costs and some degree of local attachment. In this respect, Americans are considered to be the most mobile, as they are very willing to drop everything to pursue better opportunities while the housing market is, usually, very fluid. In fact, the perception is that this mobility has even increased in the US and that it has been hampered only in the last few years, due to the current difficulties in selling homes.

Raven Molloy, Christopher Smith and Abigail Wozniak take a close look at the data and dispel some of those perceptions as myths. In fact, US internal migration has been in a steady decline for thirty years, a decline that in apparent whichever way you look at the data: by socioeconomic household characteristics and distance moved. And this has change little with the current crisis, probably because the additional incentive to move (as there is substantial evidence that some structural mismatch, including a geographic mismatch, has increased the unemployment rate recently) has been roughly compensated by the poor saleability of homes. Still, internal migration rates are still higher than almost everywhere else.

The polygyny-slave trade connection

Polygyny, a male marrying several females, is now rare except for Africa and especially Western Africa. Why would it be so prevalent in West Africa? To sustain polygyny, one needs an unbalanced sex-ratio, which is not the case there.

John Dalton and Tin Cheuk Leung claim that this is just a matter of very persistent institutions. Indeed, the sex-ratio used to be unbalanced for extensive periods in West Africa, and in a more pronounced and persistent way than anywhere else, due to the slave trade. Indeed, it took away many males from the region through the actual forced emigration, but also because of the many tribal wars associated with slave capture raids (which Dalton and Leung do not take into account).

The military draft, mortality and education

The data sometimes work in mysterious ways and provide puzzling correlations that lead to interesting research questions. One such correlation is that exemption from military service leads to lower mortality later in life.

Piero Cipollone and Alfonso Rosolia find this while looking at a natural experiment following the 1981 earthquake in Southern Italy. Boys from the affected region were exempted from military service, and they were followed, along with non-exempted neighbors, to track their life and education. By concentrating on boys both sides close to the border of the exempt region, they find that those exempt ended up being more educated. I can easily believe that, as they were not spending some of their prime learning years hiding in bushes and peeling potatoes, and they were expecting a longer work life. But the exempt also have lower mortality. This is not due to a lower incidence of military accidents, it is rather linked to the higher school completion rates. In fact, the authors conclude that raising high school completion by 10 percentage points would lower mortality by one or two percentage points in the decade thereafter. That is impressive at that age.

The child quality/quantity trade-off in the Industrial Revolution

Non-economists cringe when they hear us talking about investment in children and the quantity/quality trade-off in this regard. Yet, this is a very real aspect of child rearing pointed out by Gary Becker that is at the core of many models, and has been found wild in nature. This trade-off is though to be an integral part of the demographic transition, where fertility suddenly drops massively in the course of development.

Marc Klemp and Jacob Weisdorf look at data from Anglican parish registers from the 18th century that contain all sort of demographic data to look at the child quality/quantity trade-off during the Industrial Revolution. Theory tells us that if the returns to education and/or the cost of time (wages) get larger, parents switch from having many children with no education to few of them with better education. Klemp and Weisdorf's data indicates clearly that this trade-off is present: each additional sibling reduces by 8% the probability of a child eventually becoming literate. That is a strong effect, in particular considering the larger number of children at the time, and its rather large standard deviation during this time of transition.

Fertility differences and agricultural techniques

There are times when you read a paper and you really wonder how the authors came up with the idea to check out a particular correlation in the data, because it seems to be so far-fetched. But thus a correlation can be beautiful if it also has a nice theory that comes with it.

The correlation that Alberto Alesina, Paola Giuliano and Nathan Nunn study is between current fertility and adoption of plough agriculture in history. OK, I did not think about that one. But now that they find a nice positive correlation, how could one explain it? They argue that this has to do that women and children are not particularly useful when ploughing, as strength is required. The traditional task of weeding, that fell on women and children, is not necessary with ploughing. Thus, there is a preference for fewer children that is ingrained in the culture of these regions to this day.

Fertility and self-control

The Beckerian theory of fertility decisions in the family is based on the rationality and self-control of the involved parties, which is in stark contrast of the Malthusian theory of population growth, which relies on people breeding without control. As so often, the truth lies somewhere in between, as it is clear people guide their fertility outcomes but their is a substantial stochastic element to it.

Bertrand Wigniolle reinterprets Becker's theory by adding lack of self-control in the for of hyperbolic discounting, that is, discounted values fall rapidly in the near future and more slowly for the distant future. Wigniolle uses a three period model with parents valuing number and quality of children. In period 1, they choose the number of children and pay time costs for rearing them. In period 2, they choose their education, and support the associated costs. In period 3, they only enjoy their children. Hyperbolic discounting implies that every period they regret some of their past choices. The model yields very different results depending on parameter values. If parents have grounds to invest in the education of their children, then fertility is lower due to the lack of self-control. Call this a developed economy. If parents have no reason to invest in education (say because its return is low), then fertility gets higher with hyperbolic discounting. Call this a developing economy. And this is very sensitive to parameter values. A further reason to push for more schools and opportunities to use human capital in developing economies.

Rent seeking in divorce

Divorce is breaking a marriage, and courts rule on the compensation of the involved parties. In countries where no-fault divorce is allowed, how compensation is allocated is very much dependent on the outside option of each party, particularly when negotiations happen without the involvement of a judge, who is then just a threat point. For example, when there is only consensual divorce allowed, the partner not seeking divorce has all the bargaining power. But when no-fault unilateral divorce is allowed, the roles are completely reversed.

Sietse Bracke, Koen Schoors and Gerd Verschelden study how the introduction of unilateral divorce changes outcomes in Belgium, where consensual divorce was already permitted. In particular they look at self-sacrifice, for example how some household member may specialize in home production and thus jeopardize her labor market potential and bargaining position in case of divorce, especially when there is no-fault unilateral divorce. Indeed, one can view this specialization as an investment in future rents from marriage, and divorce annihilates those.

To analyze this, the authors collected survey data from divorces in four cities for a year. Using alimony as a signal of bargaining power, they find that alimonies are higher or more likely for long marriages, for no-fault divorces, and when there is significant self-sacrifice. That would all be consistent by theory, but unfortunately these results are somewhat tainted by the fact that the law gives judges very similar directives for handling divorces outcomes.

Breastfeeding and cognitive skills

Breastfeeding is now almost universally promoted as the healthiest way to feed a baby. And indeed, while breastfed babies are a little smaller and than bottle-fed ones and gain a little less weight, they are healthier, it is thought mainly because the mother milk transmits antibodies and relevant nutrients. But not every mother breast feeds, maybe because not every mother realizes all the benefits, or because some of the costs are high (time management for working mothers or aesthetic issues). Or there are some other benefits that are not well known.

Maria Iacovou and Almudena Sevilla-Sanz report that breastfeeding has significant positive impacts on cognitive skills (reading, writing and mathematics). While this correlation is well known, it may be spurious because mothers who breastfeed are more likely to be well educated (Irish example), and their children are also more likely to be well educated as well. The obvious way to overcome this statistical issue, a randomized trial, is not feasible on ethical grounds. What Iacovou and Sevilla-Sanz do is use propensity score matching, which essentially matches babies that have the same characteristics but breastfeeding and then compare their cognitive skills. What is particularly impressive in this study is that the retained characteristics are very broad beyond baby demographics and health, including parent characteristics such as education, job, income, and even pre-birth attitude towards breastfeeding or home and neighborhood. And even after controlling for all these variables, the impact of breastfeeding is still significant on babies from Bristol (England), and it may even grow with age.