CVD Prevention

This document describes two essential components of a disease modeling approach: how risk groups are defined and calculated, and how interventions modify incidence. The explanations focus on conceptual processes and logic without referencing specific code. ## Used in

CVD prevention strategies are incorporated as a risk factor in the following disease models:

• CVD

Mechanism

1. Risk Group Definitions and Calculations

1. Identification of Risk Factors
   The model uses demographic and epidemiological inputs to establish distributions for multiple factors such as systolic blood pressure, cholesterol levels, body mass index, and smoking status. These factors are considered simultaneously for each age and sex category.

2. Population Sampling
   A correlated sampling method generates plausible joint values for the risk factors within each subgroup. This step captures how risk factors vary together at the population level.

3. Threshold-Based Assignment
   Each simulated individual is assigned to a risk group based on the WHO PEN risk charts if relevant risk factors exceed predefined cut points. One factor surpasses a threshold. Multiple factors can surpass thresholds as well. Examples include:

   • Total cardiovascular risk under 10%
   • Total cardiovascular risk from 10% to 20% combined with systolic blood pressure above 140
   • Total cardiovascular risk above 20% combined with systolic blood pressure above 130

4. Prevalence in Each Group
   After assignment, the model determines the fraction of the population in each risk group. These fractions are stored and used for subsequent calculations, including incidence estimation and intervention effects.

2. Incidence Modification Through Interventions

1. Coverage Dynamics
   Each intervention has a baseline coverage and a target coverage. The population in need is identified by age, sex, and relevant risk factors. Coverage moves from baseline to target over a defined timescale.

2. Impact Factor
   An intervention includes a percentage impact that lowers incidence among individuals who receive it. For example, "Prevention of SBP 140 TR 20" applies a specific reduction to individuals with systolic blood pressure above 140 and total risk above 20%. This impact factor is a measurable fraction by which the intervention decreases the transition into disease.

3. Population Reached
   The coverage fraction is multiplied by the population in need to calculate how many individuals actually receive the intervention. Incidence for those reached is then adjusted by the specified impact factor.

4. Adjustment of Incidence
   The baseline incidence for a risk group is modified according to coverage and impact. A typical calculation involves a multiplicative step that lowers the original incidence:

   new incidence = baseline incidence × (1 - (impact factor × coverage))

Interventions

CVD Interventions in Appendix 3

Assumptions