“…A usual strategy to study their interactions is to design a structural model, in general including speci…c equations for fertility, mortality, real wages and population growth and to estimate the parameters of these equations. Several models of this kind have been proposed and, although in essence they are very similar, each model tends to include di¤erent sets of variables, presents its own version of the structural equations and is estimated with di¤erent econometric techniques (Lee 1985b, 1993, Tsoulouhas 1992, Bailey and Chambers 1993. There is another approach in which, instead of de…ning a priori an underlying structural model, researchers simply represent each variable as a function of the actual and lagged values of the other variables but, of course, at the cost of imposing other kinds of restrictions to identify the relevant interactions.…”