title: Quantitative risk stratification in Markov chains with limiting conditional distributions.
abstract: BACKGROUND
  Many clinical decisions require patient risk stratification. The authors introduce the concept of limiting conditional distributions, which describe the equilibrium proportion of surviving patients occupying each disease state in a Markov chain with death. Such distributions can quantitatively describe risk stratification.
  
  
  METHODS
  The authors first establish conditions for the existence of a positive limiting conditional distribution in a general Markov chain and describe a framework for risk stratification using the limiting conditional distribution. They then apply their framework to a clinical example of a treatment indicated for high-risk patients, first to infer the risk of patients selected for treatment in clinical trials and then to predict the outcomes of expanding treatment to other populations of risk.
  
  
  RESULTS
  For the general chain, a positive limiting conditional distribution exists only if patients in the earliest state have the lowest combined risk of progression or death. The authors show that in their general framework, outcomes and population risk are interchangeable. For the clinical example, they estimate that previous clinical trials have selected the upper quintile of patient risk for this treatment, but they also show that expanded treatment would weakly dominate this degree of targeted treatment, and universal treatment may be cost-effective.
  
  
  CONCLUSIONS
  Limiting conditional distributions exist in most Markov models of progressive diseases and are well suited to represent risk stratification quantitatively. This framework can characterize patient risk in clinical trials and predict outcomes for other populations of risk.
authors.affiliation: Department of Economics, Massachusetts Institute of Technology, Cambridge, MA, USA. dcchan@partners.org
authors.forename: David C
authors.initials: DC
authors.lastname: Chan
authors.forename: Philip K
authors.initials: PK
authors.lastname: Pollett
authors.forename: Milton C
authors.initials: MC
authors.lastname: Weinstein