Variable rules analysis is a set of statistical analysis methods in linguistics that are commonly used in sociolinguistics and historical linguistics to describe patterns of variation between alternative forms in language use. It is also sometimes known as Varbrul analysis, after the name of a software package dedicated to carrying out the relevant statistical computations. The method goes back to a theoretical approach developed by the sociolinguist William Labov in the late 1960s and early 1970s, and its mathematical implementation was developed by Henrietta Cedergren and David Sankoff in 1974.