Salvucci synthesized all the major studies of language variation over space from 1968 to the late 1990s. More important: what is prestigious is one community may be a mark of disloyalty and highly stigmatized in the next, and thus the simplest truth about language variation: a speaker will gravitate to the variants tied to the community which is most important to him or her, despite possible negative repercussions. The fact is, some people strive for economic success and socially upward movement, but resist assimilation to the language habits of others who have successfully achieved that goal. Michael Silverstein proposed the concept of indexical order as an alternate way of studying language variation and change. Sociolinguists are especially interested in how the stages of the Northern Cities Chain Shift relate to each other, and how they are motivated.