DOCUMENTATION.md

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1. Overview of the Model

This document describes the WHO - MSD - Anxiety model, which is a botech implementation of the Spectrum Anxiety Model.

The primary purpose of this model is to simulate the progression of anxiety disorders within a population and to understand the potential impact of various interventions. It helps to model how an individual's health status regarding anxiety can change over time, moving between states such as being healthy, having an anxiety episode, receiving treatment, or recovering.

By simulating these processes, the model can assist decision-makers in understanding the potential effects of different health programs and interventions aimed at addressing anxiety. This can help in planning and allocating resources more effectively. The model runs from the year 2025 to 2050.

2. The Model's Building Blocks: Population Groups and How They Connect

The model is constructed from various components that represent different population segments, health states, and influential factors. These are connected to show how the population's health can change.

a. Population Groups and Key Factors (Nodes):

The model uses "states" or "groups" (called nodes) to represent different segments of the population or important factors that influence health.

Key population groups (STATE nodes) in this model include:

• DsFreeSus: This group represents the healthy population, susceptible to developing anxiety but currently free of the disease.
• AnxietyEpsd: This group represents individuals who are currently experiencing an anxiety episode.
• Deceased-DsFreeSus: This represents individuals from the "DsFreeSus" group who have passed away due to general mortality.
• Deceased-AnxietyEpsd: This represents individuals from the "AnxietyEpsd" group who have passed away.
• Healthy Years Lived: This is a special state that accumulates the healthy years lived by the population, considering the impact of disability.

Other important nodes represent fixed numbers, rates, or intermediate calculations:

• CONSTANT nodes: These are fixed values or rates used as inputs. Examples include:
  • Anxiety_Disability_Weight: A fixed value representing the disability associated with an anxiety episode.
  • AnxietyEpsd_Incidence_Rate: The baseline rate at which new cases of anxiety episodes appear in the healthy population, based on data for the specified country and condition.
  • AnxietyEpsd_Remission: The baseline rate at which individuals with an anxiety episode recover, based on data for the specified country and condition.
  • AntiDepressantBasicPsychMild_Disability_Impact: The reduction in disability due to the "Basic psychosocial support for mild cases" intervention. Similar nodes exist for other interventions and their impact on disability or remission.
  • AntiDepressantBasicPsychMild_Coverage: The proportion of the eligible population reached by the "Basic psychosocial support for mild cases" intervention. This can change over time. Similar nodes exist for other interventions.
• SURROGATE nodes: These are temporary holding places for calculations that help the model progress. For example:
  • AnxietyEpsd Incidence: A temporary store for the number of new anxiety cases calculated in a time step before they are added to the "AnxietyEpsd" group.
  • AnxietyEpsd Remission: A temporary store for the number of people recovering from anxiety in a time step.
  • DsFreeSus HYL: A temporary calculation for the healthy years lived by the "DsFreeSus" group.
• FUNCTION nodes: These nodes perform calculations based on their inputs. Examples include:
  • Combined_HYL: Calculates the overall health-adjusted life years, considering disability weights and intervention effects.
  • Disability_Effect_Transform: Calculates the combined effect of interventions on reducing disability.
  • Births: Stores the number of births occurring in the population during a time step.

b. Connections and Movements (Links):

"Links" show how people move between population groups or how factors influence each other.

Key connections in the model include:

• Population Dynamics:

  • DsFreeSus -> Births and AnxietyEpsd -> Births: These links calculate the number of births from individuals in the "DsFreeSus" (healthy) and "AnxietyEpsd" groups, respectively. This is based on fertility rates from the specified country. The total births are stored in the "Births" node.
  • Births -> DsFreeSus: New male and female births are added to the "DsFreeSus" (healthy) population group. This uses sex ratio data for the specified country.
  • Migration - DsFreeSus and Migration - DsFreeSus (for AnxietyEpsd state): These links adjust the number of people in the "DsFreeSus" and "AnxietyEpsd" groups to account for people moving into or out of the area, based on national migration data.
  • BackgroundMortality DsFreeSus (DsFreeSus -> Deceased-DsFreeSus) and Background Mortality AnxietyEpsd (AnxietyEpsd -> Deceased-AnxietyEpsd): These links move individuals from the "DsFreeSus" and "AnxietyEpsd" groups to their respective "Deceased" states. This movement is based on general death rates obtained for the specified country. People are removed from the source group.

• Anxiety Progression and Recovery:

  • Prevalence DsFreeSus -> AnxietyEpsd: This link represents the initial allocation of the population into the "AnxietyEpsd" state based on existing prevalence data for the specified country and condition. People are moved out of "DsFreeSus".
  • AnxietyEpsd_Incidence_Rate -> DepressionEpsd Incidence (influences AnxietyEpsd Incidence -> AsthmaEpsd): New cases of anxiety arise from the "DsFreeSus" group and move to the "AnxietyEpsd" group. The rate is determined by AnxietyEpsd_Incidence_Rate.
  • AnxietyEpsd_Remission_Rate -> DepressionEpsd Remission (influences AnxietyEpsd Remission -> DsFreeSus): Individuals in the "AnxietyEpsd" group can recover and move back to the "DsFreeSus" group. The base rate is determined by AnxietyEpsd_Remission. This rate can be modified by intervention effects.

• Intervention Effects on Disability and Remission: The model includes several interventions, such as "AntiDepressantBasicPsychMild" (Basic psychosocial support for mild cases), "AntiDepressantBasicPsychModerate" (Basic psychosocial support and anti-depressant medication for moderate-severe cases), and "AntiDepressantIntensPsych" (Psychological treatment and anti-depressant medication for moderate-severe cases).

  • Links like AntiDepressantBasicPsychMild_Disability_Impact -> AntiDepressantBasicPsychMild_Disability_Effect: The inherent disability reduction efficacy of an intervention (AntiDepressantBasicPsychMild_Disability_Impact) is combined with its coverage (AntiDepressantBasicPsychMild_Calculated_Coverage) and population in need (AntiDepressantBasicPsychMild_PIN) to determine the overall AntiDepressantBasicPsychMild_Disability_Effect. This effect then influences the Combined_DW (Combined Disability Weight). Adherence (e.g., AntiDepressantBasicPsychMild-Adherence -> AntiDepressantBasicPsychMild_Disability_Impact) also modifies the intervention's impact.
  • Links like AntiDepressantBasicPsychMild_Remission_Impact -> AntiDepressantBasicPsychMild_Remission_Effect: Similarly, the remission efficacy of an intervention is combined with coverage, PIN, and adherence to calculate its overall effect on remission. This modifies the AnxietyEpsd Remission rate.
  • These effects are aggregated. For instance, AntiDepressantBasicPsychMild_Disability_Effect -> Disability_Effect_Transform shows individual intervention effects contributing to an overall transformation factor for disability.

• Calculating Health Outcomes (DALYs, HYL):

  • Anxiety_Disability_Weight -> Anxiety_HYL and Healthy_Disability_Weight -> Healthy_HYL: These links help calculate the health-adjusted life years (HYL) by subtracting the disability weight from a full healthy year.
  • DsFreeSus HYL -> Healthy Years Lived and AnxietyEpsd HYL -> Healthy Years Lived: The HYL for each state are summed up in the "Healthy Years Lived" node.
  • The model also calculates Years Lived with Disability (YLDs) for each state (e.g., YLD-AnxietyEpsd, YLD-DsFreeSus) and Years of Life Lost (YLLs) (e.g., YLL-AnxietyEpsd, YLL-DsFreeSus). These components are then summed into a "DALYs" (Disability-Adjusted Life Years) node. For example, Deceased-DsFreeSus -> YLL-DsFreeSus records YLLs when individuals from the "DsFreeSus" group die.

• Resource Utilization:

  • Links like PopulationReached-AntiDepressantBasicPsychMild -> Outpatient visit with Staff Nurse: When individuals receive an intervention (represented by "PopulationReached" nodes like PopulationReached-AntiDepressantBasicPsychMild), this triggers resource use. This specific link calculates the number of outpatient visits with a staff nurse required for the "Basic psychosocial support for mild cases" intervention.
  • Outpatient visit with Staff Nurse -> Staff Nurse Minutes: The number of visits then determines the total staff nurse minutes required.
  • Staff Nurse Minutes -> Staff Nurse Minutes Cost: These minutes are then translated into costs.
  • Similar links exist for other resources like different types of health personnel (Enrolled Nurse, Professional Nurse, Doctor), medicines (Fluoxetine, Citalopram), and facility stays (Inpatient Stay).

This structure allows the model to simulate how the population moves between health states, how interventions affect these transitions and outcomes, and what resources are consumed.

3. How the Model Simulates Changes Over Time (Subroutines)

The model simulates changes year by year (or for other defined time periods) by following a sequence of steps, called "subroutines." Here's what happens in each main step:

• Flush unneeded values: This step resets or clears out temporary values from the previous time period to prepare for new calculations.
• Generate the population: This step sets up the initial numbers of people in the main healthy population group ("DsFreeSus") at the beginning of a time period.
• Allocate prevalence: This step distributes the initial population into the "AnxietyEpsd" state based on existing disease prevalence at the start of the simulation (for the first year) or adjusts based on incidence in subsequent years.
• Generate the base values of the surrogate nodes: Calculates starting values for temporary holding places used in calculations (e.g., for new cases, remissions, HYL contributions).
• Generate the base values of the function nodes for constants: Sets up initial values for nodes that perform calculations based on other inputs.
• Generate the values of the constants: Loads or calculates fixed input values like disability weights, baseline incidence/remission rates, and intervention characteristics (coverage, efficacy).
• Modify the impact (efficacy) by the adherence: Adjusts the effectiveness of interventions based on how well people adhere to treatment.
• Calculate the Incidence Surrogate: Computes the number of new anxiety cases based on the incidence rate.
• Calculate the remission surrogate: Computes the number of people recovering from anxiety based on the remission rate.
• Calculate Coverage: Determines the actual coverage levels for each intervention, considering baseline, target, and scale-up parameters.
• Calculate Disability Effects: Computes the impact of interventions on reducing the disability associated with anxiety.
• Add remission impact to remission effect: Combines the inherent remission efficacy of interventions with other factors.
• Modify remission effect by coverage: Adjusts the overall remission effect based on the proportion of the population reached by interventions.
• Modify remission effect by PIN: Further refines the remission effect based on the proportion of the population in need of the intervention.
• Add calculated remission impact to transform: Aggregates the remission effects of different interventions.
• Modify remission surrogate by remission effect: Adjusts the number of people recovering based on the combined impact of interventions.
• Remove Disability Effects from 1.0: This step calculates a factor representing the remaining disability after accounting for intervention effects (where 1.0 is full disability and effects reduce this).
• Calculate Healthy and Anxiety HYL: Calculates Health-Adjusted Life Years for healthy individuals and those with anxiety, considering their respective disability weights.
• Calculated Combined HYL: Aggregates HYL contributions, potentially modified by intervention effects on disability.
• Calculate Combined DW: Calculates the overall disability weight experienced by those with anxiety, considering intervention effects.
• Modify Combined DW with intervention effects: Adjusts the disability weight based on the effectiveness of interventions in reducing disability.
• Calculated Modified HYL: Calculates the final Health-Adjusted Life Years for those with anxiety after accounting for intervention-modified disability.
• Calculate DsFreeSus Disability Surrogate: Calculates HYL for the healthy, susceptible population.
• Calculated Anxiety HYL Surrogate: Calculates HYL for the population with anxiety episodes, considering modified disability.
• Record Births to Birth Node: The model calculates the number of births occurring in both healthy and anxiety-affected populations and stores this total.
• Main Routine (Synchronous transfer): In this core step, the model applies rates and proportions to simulate people moving between groups (e.g., from healthy to having anxiety, from anxiety to recovered, or to a deceased state). This also includes background mortality and applying migration effects.
• Push AnxietyEpsd to Population Reached: Determines the number of individuals with anxiety who are eligible for and could potentially receive each intervention.
• Modify Population Reached by PIN and Coverage: Calculates the actual number of people reached by each intervention by applying the population in need (PIN) proportions and the calculated coverage rates.
• Record HYL: The model updates the total "Healthy Years Lived" by summing contributions from different population groups.
• Add prevalence to YLD nodes: Calculates the number of people living with disability in each state for YLD calculations.
• Multiply YLDs by Disability Weights: Applies the relevant disability weights to the populations in each state to quantify YLDs.
• Migration of Populations: Adjusts population numbers in states to account for net migration.
• Age the populations: This step simulates the entire population in each state getting older by one time unit (e.g., one year).
• Women give birth: New births (calculated earlier) are added to the healthy population group, distributed by sex.
• Add values to DALYs: This step aggregates YLDs and YLLs to calculate the total DALYs.
• Calculate resource requirements and costs: Based on the number of people receiving interventions, this step calculates the demand for various resources (personnel time, medicines, visits) and their associated costs.
• Record Metrics: This step records important results and numbers from the model for the current time period, such as population sizes in different states, DALYs, HYL, and resource utilization.

This sequence is repeated for each year of the simulation, allowing the model to project changes in population health and intervention impact over time.

4. Resource Requirement Assumptions

The model incorporates specific assumptions about the resources needed for each intervention. These are detailed below for each intervention type:

Intervention 1: Basic psychosocial treatment for anxiety disorders (mild cases)

Target Population Node in Model: PopulationReached-AntiDepressantBasicPsychMild

Personnel Time Required per Case:

• 100% of cases receive two 20-minute visits with a staff nurse.
• During the first visit: 5 minutes of Enrolled Nurse (EN) time for basic screening during vitals.
• During the first visit: 5 minutes of Professional Nurse (PN) time required for APC (Assessment, Planning, Care) assessment.

Visits or Inpatient Time Required per Case:

• 2 outpatient visits.

Intervention 2: Basic psychosocial treatment and anti-depressant medication for anxiety disorders (moderate-severe cases)

Target Population Node in Model: PopulationReached-AntiDepressantBasicPsychModerate

Drugs and Supplies required Per Client:

• Fluoxetine, 20 mg tab: 75% of cases receive this, 1 unit per day for 180 days (total 180 units per case).
• Citalopram, 20mg tab: 25% of cases receive this, 1 unit per day for 180 days (total 180 units per case).

Personnel Time Required per Case:

• 100% of cases receive two 20-minute visits with an Enrolled Nurse (EN) for psychosocial support.
• 100% of cases receive one 10-minute visit with a nurse for medication management.
• 100% of cases receive one 10-minute visit with a doctor (generalist or specialist, depending on setting) for medication management.
• During the first visit: 5 minutes of EN time for basic screening during vitals.
• During the first visit: 5 minutes of PN time required for APC assessment.

Visits or Inpatient Time Required per Case:

• 100% of cases have 2 outpatient visits.
• 2% of cases will require hospitalization for 14 inpatient days.

Intervention 3: Intensive psychosocial treatment and anti-depressant medication for anxiety disorders (moderate-severe cases)

Target Population Node in Model: PopulationReached-AntiDepressantIntensPsych

Drugs and Supplies required Per Client:

• Fluoxetine, 20 mg tab: 75% of cases receive this, 1 unit per day for 180 days (total 180 units per case).
• Citalopram, 20mg tab: 25% of cases receive this, 1 unit per day for 180 days (total 180 units per case).

Personnel Time Required per Case:

• 100% of cases receive one 10-minute visit with a nurse for medication management.
• 100% of cases receive one 10-minute visit with a doctor for medication management.
• During the first visit: 5 minutes of EN time for basic screening during vitals.
• During the first visit: 5 minutes of PN time required for APC assessment.
• 90% of cases receive 8 individual psychosocial therapy sessions, each lasting 50 minutes, delivered by an enrolled nurse.
• 10% of cases receive 2 individual psychosocial therapy sessions, each lasting 50 minutes, delivered by an enrolled nurse.
• 10% of cases (the same 10% receiving fewer individual sessions) receive 8 group psychosocial therapy sessions, each lasting 50 minutes, delivered by an enrolled nurse (to a group of 5 participants).

Visits or Inpatient Time Required per Case:

• 100% of cases have 2 outpatient visits for medication.
• 90% of cases have 8 outpatient visits for individual therapy.
• 10% of cases have 10 outpatient visits (2 individual + 8 group) for therapy.
• 2% of cases will require hospitalization for 14 inpatient days.

(Note: Intervention 4 details were provided but did not have a corresponding "PopulationReached" node in the model's resource links, so it is not detailed here as its resources are not directly connected in the provided model structure).

5. Coverage Assumptions for Scenarios

The model can be run under different scenarios, each with specific assumptions about intervention coverage levels and how they change over the simulation period (2025-2050).

Scenario: Default Scenario

Description: Where default coverage rates stay the same. All relevant parameters are exposed for editing.

• Intervention: Basic psychosocial support for mild cases

  • Baseline Coverage: 5.0%
  • Target Coverage: 5.0%
  • Scale-up Period: from 2025 to 2030 (coverage remains constant at baseline)

• Intervention: Basic psychosocial support and anti-depressant medication of first episode moderate-severe cases

  • Baseline Coverage: 10.0%
  • Target Coverage: 10.0%
  • Scale-up Period: from 2025 to 2030 (coverage remains constant at baseline)

• Intervention: Psychological treatment and anti-depressant medication of first episode moderate-severe cases

  • Baseline Coverage: 5.0%
  • Target Coverage: 5.0%
  • Scale-up Period: from 2025 to 2030 (coverage remains constant at baseline)

Scenario: All-On Scenario

Description: Where all interventions are scaled up to their target coverage.

• Intervention: Basic psychosocial support for mild cases

  • Baseline Coverage: 5.0%
  • Target Coverage: 20.0%
  • Scale-up Period: from 2025 to 2030

• Intervention: Basic psychosocial support and anti-depressant medication of first episode moderate-severe cases

  • Baseline Coverage: 10.0%
  • Target Coverage: 30.0%
  • Scale-up Period: from 2025 to 2030

• Intervention: Psychological treatment and anti-depressant medication of first episode moderate-severe cases

  • Baseline Coverage: 5.0%
  • Target Coverage: 20.0%
  • Scale-up Period: from 2025 to 2030

Scenario: Basic psychosocial support for mild cases

Description: Scaling up the intervention to target coverage.

• Intervention: Basic psychosocial support for mild cases
  • Baseline Coverage: 5.0%
  • Target Coverage: 20.0%
  • Scale-up Period: from 2025 to 2030 (Other interventions remain at their default/baseline levels as per the "Default Scenario" not explicitly overridden here).

Scenario: Basic psychosocial support and anti-depressant medication for moderate-severe cases

Description: Scaling up the intervention to target coverage.

• Intervention: Basic psychosocial support and anti-depressant medication of first episode moderate-severe cases
  • Baseline Coverage: 10.0%
  • Target Coverage: 30.0%
  • Scale-up Period: from 2025 to 2030 (Other interventions remain at their default/baseline levels as per the "Default Scenario" not explicitly overridden here).

Scenario: Psychological treatment and anti-depressant medication for moderate-severe cases

Description: Scaling up the intervention to target coverage.

• Intervention: Psychological treatment and anti-depressant medication of first episode moderate-severe cases
  • Baseline Coverage: 5.0%
  • Target Coverage: 20.0%
  • Scale-up Period: from 2025 to 2030 (Other interventions remain at their default/baseline levels as per the "Default Scenario" not explicitly overridden here).