The intuitive background for measures of structural previous termcentralitynext term in previous termsocial networksnext term is reviewed and existing measures are evaluated in terms of their consistency with intuitions and their interpretability. Three distinct intuitive conceptions of previous termcentralitynext term are uncovered and existing measures are refined to embody these conceptions. Three measures are developed for each concept, one absolute and one relative measure of the previous termcentralitynext term of positions in a previous termnetwork,next term and one reflecting the degree of centralization of the entire previous termnetwork.next term The implications of these measures for the experimental study of small groups is examined.