Similarity Indices in Community Studies: Potential Pitfalls

Four common similarity indices used in multivariate descriptive techniques, such as classifications and trellis diagrams, are compared over a range of overlap from 100 to 10 % to a theoretical standard.Only the Bray-Curtis Index (also known as Czekanowski's Quantitative Index, Proportional Similarity and a variety of other names) was found to reflect accurately true similarity.The other indices (Canberra Metric, Morisita's and Horn's Information Theory) diverge greatly from one another and from the theoretical standard.