On the advantage of marriage over cohabitation

Why marry when cohabitation can provide the same benefits of economies of scale and companionship? One may even think that cohabitation is superior because it allows a break up with less consequences. That is exactly wrong. The fact that divorce is costly makes that one is more careful in committing to marriage and, once married, one puts more effort into the marriage. The key here is that marriage is a commitment device that gives strong incentives to make a marriage work.

Murat Iyigun shows that this logic gives marriage a large surplus than cohabitation through spousal commitment, as long as men and women are available in roughly equal numbers and commitment costs are symmetric across genders. Otherwise, marriage surpluses collapse and cohabitation dominates.

The fact is that commitment costs are not equal, mostly because of children and traditional roles in the household and the labor market. In fact, the countries where women are the most equal to men (say, Scandinavia) are those where cohabitation is the most prevalent. That evidence goes exactly counter to the predictions of the Iyigun model. Unfortunately, the paper provides absolutely no empirical support for its results. In fact, it is not even motivated by any empirical fact that would need to be explained. What is it then good for?