Extending Gower's general coefficient of similarity to ordinal characters

The possibilities of calculating similarity based on ordinal characters are evaluated by distinguishing subtypes of the ordinal scale. Multivariate an alysis is most problematic when ordinal variables appear together with othe r scale types in the data. This difficulty is solved by extending Gower's g eneral coefficient of similarity to ordinal data types, facilitating cluste r analysis and multidimensional scaling. Two alternatives, a non-metric and a metric version, are offered. The modified formula implies that ordinal v ariables are equally weighted with the others, and that partially and fully ranked data are both applicable, due to the inherent standardisation proce dure. A morphological data set derived for the moss genus Tortula illustrat es the new approach.