Why Pearson's r is Not a Good Similarity Coefficient for Comparing Collections

Pearson's coefficient of linear correlation, r , sometimes is used to express the similarity between two archaeological collections when each collection is characterized by the percents of the artifact types it includes. Examples show that r can be extremely misleading when used in this way, and patterns of similarity among a group of collections can be wildly misrepresented. The Brainerd–Robinson statistic is one example of a similarity coefficient that is much better than r for comparing collections.