IMA Journal of Management Mathematics Advance Access published online on December 3, 2008
IMA Journal of Management Mathematics, doi:10.1093/imaman/dpn031
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Analytical methods for calculating the distribution of the occupancy of each state within a multi-state flow system



Clinical Operational Research Unit, University College London,Gower Street, London WC1E 6BT, UK
Department of Health Sciences, University of York, Heslington, York YO10 5DD, UK
Corresponding author. Email: m.utley{at}ucl.ac.uk
Email: s.gallivan{at}ucl.ac.uk
Email: c.pagel{at}ucl.ac.uk
¶ Email: dr17{at}york.ac.uk
Received on 1 May 2007. Accepted on 1 January 2008.
We present analytical techniques for estimating the time-varying occupancy of each state within any multi-state flow system that can be represented as a particular type of directed graph called a rooted directed tree. Such systems have a single point of entry from which each other state within the system can be reached by exactly one directed path. The discrete-time model presented incorporates the use of time-varying and general distributions for the number of individuals entering the system and of general sojourn time distributions for each state. We illustrate the use of such analysis in the context of the delivery of mental health services in the community for people with common mental health problems and then discuss the possibility of adapting these methods with relation to systems that have a structure more complex than that of a rooted directed tree.
Keywords: stochastic analysis; capacity planning; patient flow; rooted directed trees; compartmental models