Lefkovitch, L. P. 1965.
Lefkovitch, L. P. 1965. The study of population growth in organisms grouped by stages. Biometrics, 21: 1–18.
(tomato del artículo)
In this extension to the use of matrices in population mathematics (Lewis  and Leslie ), the division of a population into equal age groups is replaced by one of unequal stage groups, no assumptions being made about the variation of the duration of the stage that different individuals may show. This extension has application in ecological studies where the age of an individual is rarely known. The model is briefly applied to three experimental situations.