6 innovators, the access to a rich data set has allowed us to develop an integrated model incorporating their separate contributions. The Easterlin framework which incorporates the demand for children, natural fertility and the cost of fertility regulaiiori is intuitively appealing, and the process of demographic transition which it sketches out provides useful insights.

In the early stages of demographic transition the supp)y of living children is below the desired level of fertility and thus fertility is constrained by natural fertility. As survival rates improve and the process of development lowers the family size preferences of the couple, actual fertility will exceed desired fertility. Initially, family planning will not be used because of its perceivsd high or actual costs and because actual fertility continues to be determined by natural fertility. Eventually, fertility regulation is ad^pted and actual fertility falls below natural fertility, but slill exceeds the dernand for children. When the costs of regulation become negligible, actual fertility equals the demand for children. From the point at which the unregulated supply of surviving births begins to exceed the demand for children, the cost of fertility regulation can be said to be a constraint on fertility decline.

As appealing as this framework is, there are a number of problems with testing it empirically. The main dimensions of the model are all subjiect to more or less serious problems of measurerm -nt. Easterlin and Crimmins in various papers have measured demand bv desired familv size, and have est mated natural fertility by estimates of regression equations with various proximate determinants and cost of regulation as various as the woman's knowledge of contraception or community access to family planning. Their results have tended to show the significance of both the difference between natural fertilitv and desired fertility and the cost of fertility regulation. The relative importance of these factors have varied, however, from place to place.

Schultz has criticized the work by Easterlin in several ways: 1) he rejects the usefulness of the concept of desired family size, and 2) he rejects the technique used by Easterlin to estimate natural fertility. His rejection of desired family size is in part an economist's hesitation to take what people say at face value and in part the belief that desired family size is in fact endogenous with respect to the costs of fertility regulation. His rejection of the Easterlin technique for estimating natural fertility arises from his belief that the recursive method used by Easterlin to estimate natural fertility leads to biases in the estimation of the effect of contraception use on fertility and thus it underestimates the natural supply of children. In Rosenzweig and Schultz (1985), the authors use U.S. data to ,>;strate how a simultaneous model which allows for couples to adjust their contraceptive behavior on the basis of their perceptions of their own fertility leads to a larger magnitude of effects of usage on fertility since more fecund couples are more likely to adopt contraception earlier and use more reliable methods.

In this paper, we use a model which, 1) incorporates desired family size, but allows us to test whether it is in fact affected by access to family planning services as well