Birth order effects and time allocation.Res Popul Econ. 1991; 7:191-213.RP
"In this paper, a model is developed in which the explanation for birth-order effects does not rely on absence of capital markets, but follows from optimal allocation of parental time and goods among children over the childrearing years. The model yields two key results, which are then tested using 1967-1968 household survey data from urban Colombia.... It is shown that first and last-born children of mothers who do not work have an advantage over middle-borns.... At the same time, as predicted, there are no differences by birth order among children of working mothers. The persistence of birth-order effects even in high-income families indicates that such effects are at least in part due to the time constraint modelled; this is a strong result given the possibility of better substitutes for mother's time than allowed for in the model, and the likelihood that high-income families are able to purchase better substitutes."