Dear all Suppose A1,A2,...,A8 are primary units (PSU) of a two stage sampling and Ai (i=1,2,...,8) include 3 clucter (or panel). How can we select one claster of per Ai by rotation sampling as in per times selection (for 8 selection) 1/8 of clusters are swaped with new clasters. Zahedian %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%