TOWARDS STOCHASTIC FORECASTS OF THE ITALIAN POPULATION: AN EXPERIMENT WITH CONDITIONAL EXPERT ELICITATIONS

The work reports on the whole process developed to produce expert-based stochastic forecast of the Italian population for the period 2011-2065. We follow the method proposed by Billari et al. (2012), where the full probability distribution of forecasts is specified on the basis of expert opinions on future developments of the main components of the demographic change. In particular, we derive the joint forecast distribution of the pair Total Fertility Rate and Immigration, on one side, and of the pair Male and Female Life Expectancy at Birth on the other side. The distribution of Emigration and Mean Age at Birth are derived separately. The conditional elicitation procedure makes it possible to derive information on the marginal behaviour of a single indicator in terms of expected value and variability, but also on the across time correlation of each indicator and on the correlation between any two indicators at a given year or across time. Any indicator is then prorated in term of age specific values, the distribution of which is obtained resorting to well-known and widely used demographic models. We show the main results of this experimental project, covering the projected distribution for indicators of the demographic behaviour, for the total population and for age related population indicators. In specifying the probabilistic distribution of each indicator, we discuss the problems that can arise in the collection of expert opinions and the solutions that can be implemented in order to avoid inconsistencies in the calculation of the parameter.