Cost effectiveness and strategic planning (WHO-CHOICE)

Generic 4-state disease population model (PopMod)

Population Model

In order to estimate the population-level impact of different health interventions, the population model PopMod tracks a whole population (such as a whole country or WHO sub-region) over a period of 100 years. Specifically, PopMod enables the analyst to model the incidence / prevalence, remission and case-fatality associated with a given disease or risk factor, both under the situation of no health care and also under the situation of one or more effective interventions being in place (at a specified level of coverage). In this way, it is possible to establish the population-level health gain (or disease burden averted) as a result of a given intervention, relative to doing nothing.

The following diagramme illustrates the schema used in PopMod for modeling disease. The figure shows the full model, although a reduced model that does not incorporate the effects of comorbidity can also be specified. Intervention effectiveness works on one or more of the specified hazard rates in the model (incidence, remission, case fatality) or on the health state valuation of a health condition.

Generic 4-State Disease Population Model

Generic 4-State Disease Population Model

Notes

X is the population group with condition X
C is the population group with condition C
XC is the population group with the joint condition XC
S is the population group with neither condition X nor C ("healthy" or "susceptible" population) D is deaths

ix2 is flow to XC from C (incidence to X)
rx1 is flow to S from X (remission from X)
rx2 is flow to C from XC (remission from X)
ic1 is flow to C from S (incidence to C)
ic2 is flow to XC from X (incidence to C)
rc1 is flow to S from C (remission from C)
rc2 is flow to X from XC (remission from C)

fx is flow to D from X due to cause X (case fatality of X)
fc is flow to D from C due to cause C (case fatality of C)
fxc is flow to D from XC due to cause X or C (case fatality of XC)
m is flow to D from S, X, C, or XC due to any other cause (background mortality)

B is births
T is total population
"bin 0" is the population group between 0 and 1 year of age

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For more details on the mathematical design of PopMod please read Lauer et al. (2002).