retention index (ri)
Glossary of "Cladistics (2nd ed.)" by Kitching et al. (1998)
- A measure of the amount of similarity in a character that can be interpreted as synapomorphy on a given cladogram. The retention index is calculated as the ratio of (g - s) to (g - m), where g is the greatest number of steps a character can exhibit on any cladogram, m is the minimum number of steps a character can exhibit on any cladogram and s is the minimum number of steps the same character can exhibit on the cladogram in question. See also consistency index, ensemble retention index.
Glossary of Plant Systematics (1st ed.) by Simpson (2006)
- A measure of the relative amount of homoplasy in a cladogram, equal to the ratio (g-s)/(g-m), where g is the maxjmum possible number of state changes that could occur on any conceivable tree, m is the minimum possible number of character state changes, and s, is the actual number of state changes that occur.
- Kitching, I. J., Forey, P. L. Humphries, C. J. & Williams, D. M. 1998. Cladistics, 2nd ed.: the Theory and Practice of Parsimony Analysis. -xii + 228 pp. Oxford University Press, New York.
- Simpson, M. G. 2006. Plant Systematics. -xi + 590 pp. Elsevier Academic Press, Oxford.