Transition Probabilities and Rates

Selection of initial model input parameters is an important step during model development. Input parameters are typically chosen to represent characteristics of the entire population: transitional probabilities (initiation, cessation, quitting, switching) and health outcome (mortality and/or morbidity rates). The initial values of these parameters are typically estimated from sources representative of the population, such complex probability population survey and census. 

Transition probabilities determine the rate at which the population changes with respect to time during the period of interest. For example, we might be interest in projecting the health impact of introducing a new tobacco product on the U.S population for a period of 50 years starting on year 2000; transition probabilities govern transition between tobacco use behavior as well as health outcome during the projection period (50 years in this example). The following figure shows different transition for a two-products model developed by the FDA; each letter represents a transitional probability representing transitions from tobacco use behaviors over time  

In the figure, a represents the probability of initiating product 1 while b represents the probability of initiating product 2,  and e represents the probability of initiating both products. Transition probabilities are estimated from population surveys and other sources, and they are typically tabulated by sex, age and race. In some model, these are constant during the entire simulation period, but they could also change over time.  

Mortality Rates and Risks

Another type of input parameters is those related to risk; this included mortality rates and risks related to comorbidities. For many models, these are projected over the entire simulation period (say 50 years in the future), and they are estimated from population surveys or other data sources. These parameters are tabulated base on age, sex, race, and tobacco use status.

Example 1

Birth Rate and Migration

 At each step (year for example) of the simulation period, individuals enter the population according to a birth rate that is typically....................................

Example 2