La stima della Media nel Campionamento per Centri

The "aggregation points" sampling design applies, for instance, in survey of irregular immigrants i.e. of populations composed by a finite but unknown number of units which do not consent labelling and that can be reached only through a set of known but overlapping frames called "aggregation points". Dealing with the "aggregation points" sampling design, the problem of estimating the mean of a quantitative character is concerned; an estimate of the estimator's variance is also proposed. Some results from a simulation study are presented. Simulations indicate that estimators proposed perform better in case of not too large number of aggregation points but extensively overlapping.