Practically all of formal demography deals with transitions of people from one state at a given moment to another state some time later: for example, single to married, in school to out of school, healthy to sick, in the labor force to out of the labor force, alive to dead. It has now become clear that all such transition patterns may be studied using the mathematical methods developed for the analysis of interregional migration flows within multiregional population systems. In consequence, the mathematical models of multiregional demography adopted by the International Institute for Applied Systems Analysis have been found to be applicable to a wide range of demographic topics. This article illustrates the application of these multistate models to multiple contingency calculations used in actuarial practice.
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KEYFITZ, Nathan and ROGERS, Andrei, 1982. Simplified Multiple Contingency Calculations. The Journal of Risk and Insurance. Online. 1982. Vol. 49, no. 1, p. 59–72. [Accessed 31 May 2022]. DOI 10.2307/252576 
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Kolmogorov
[6, 13]
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13. Willekens, F., The Demography of Labor Force Participation, Research Memorandum RM-78- I 7 (Laxenburg, Austria: International Institute of Applied Systems Analysis, I 978). Published in revised form in Environment and Planning A, I2:5 (1980), pp. 563-588.