Estimation of the foreigners fertility in Italy using mathematical functions

This work is a first attempt to estimate the specific fertility rates for some foreigners nationalities in Italy. The available data are the total births distributed by age of the mother for the six nationalities: Albanians, Moroccans, Romanians, Chinese, Ecuadorians and Nigerians. The age structure of women by nationality is not given. The method here proposed uses fertility theoretical curves, which depend on three important demographic indices - the total fertility, the average age at childbearing and the variance around this average age - a method already used in other past applications for different intents. We firstly hypothesized the existence of a linear relationship between the crude birth ratio and the other three parameters, estimating its value through an interpolation procedure on data from 2002 to 2005. Then we used five mathematical functions (Beta, Gamma, Lognormal, Third-degree Polynomial, Hadwiger) to fit the age specific rates distribution.