Campionamento per popolazioni rare ed elusive: la matrice dei profili

We have compared four methods (center sampling, multiple frame, network and adaptive sampling) usually proposed for samples drawn from rare and/or elusive populations, for which we haven’t a frame or, if we have, is incomplete. As the multiple frame can be considered a particular case of center sampling and adaptive a particular case of network, the comparison will be made between center and network. To make a survey on a rare and/or elusive population with L units (that are partially overlapping for the centers and completely separate for the network) and Nobservation units we will draw, at random, some units and define a “profile” for every observation unit in the first method and define a “network” in the second one. In this paper we will show that in theory one method can be considered like the other through a support known as “profile matrix”, which in population has the size NxL. Thus, using this matrix, in the center sampling a set of equal profiles can be called network, while in the network sampling a set of equal profiles can be taken for a network or more than one. This means that once the sample has been drawn, only if a set of equal profiles characterizes a single network will the numerator of the estimators proposed for the two methods will then coincide.