Typological distributions are the combined result of universal structural principles, areal diffusion, and shared descent. The core concern of quantitative typology is to disentangle and to identify these various factors.While areal and structural factors can be tested against each other in standard multivariate designs based on sample stratification, genealogical factors cannot be handled by sample stratification since about one third of all proven families (the strata needed) are isolates, i.e. count only one member. In response, typologists have since long sought to control for genealogical relations during sampling rather than during statistical testing. But available methods suffer from a number of drawbacks. Most importantly, they are not sensitive to the fact that different typological variable have different degrees of stability (genealogical dependence) within families, and that this again varies from family to family.This article proposes a refined method for genealogical control during sampling, which is based on DRYER’s (1989) proposals but is sensitive to actual distributions within genealogical units at each taxonomic level.