Indirect Estimation and Simulation Tool (IEST) Simulation

6. Simulation

The IEST uses Monte Carlo to simulate a disease process where subjects are defined by the user and followed each year until death or until the end of the simulation.

A simulation is a process where each individual in the population progresses through the states of a model, based on a random distribution. The active states for each individual at each step in time are given in the results.

6.1 Creating a Simulation

A simulation is created by defining a new simulation project. Within this project the user can define the Study/Model, the model that guides the simulation, and the Population Set as well as some other simulation parameters and additional simulation rules. The steps to create such a simulation project are:

  1. Define States to be used in simulation.
  2. Set up Parameters to be used during simulation.
  3. Set up the Model.
  4. Set up Model Transitions.
  5. Set up the Population Set.
  6. Double click 'Add New Project' in the main window.
  7. In the 'Create New Project' window, select 'Simulation', and click OK.

8. In the Project Definition form, give the Simulation a name (A).
9. Select a Primary Model in the drop-down box (B). Note that you can drill down into the model and make changes by double clicking on the model or pressing the ... button near the name.
10. Select a Population Set in the drop-down box (C). Note that you can drill down into the population set and make changes by double clicking on the population set or pressing the ... button near the name.
11. Specify the number of Simulation Steps and Repetitions (D and E).
12. To add modification rules for parameters, follow instructions below.
13. Click Save. The form can now be closed, or the simulation can be run. This will trigger validity checking of the data entered and if no error message is displayed, then the data has been saved to memory. Note that the information is not yet saved to a file.

For a video demonstration on creating a project, click here.

6.2 Simulation Rules

From within the Simulation Project form, select the appropriate tab. The tabs are ordered according to different stages in the simulation and affect the parameters types that can be modified in this stage. Parameters are added to a project from the bottom of the Simulation Project form (F).

  • [Drop-box 1] - parameter to be used. This corresponds to the Affected Parameter column. Depending on the tab, this will be a Coefficient/ System Parameter, a Covariate, a Treatment Parameter, or a Cost/Quality of Life (QoL) parameter. For more information on parameter types, see Parameters.
  • If in State - a conditional. The function will only be carried out when the individual is in that particular state.
  • Occurrence Probability - probability that the function will be implemented
  • Function - computational expression, which can use parameters as variables. Note that the expression used here will be calculated only at runtime during the simulation and the value evaluated will be assigned as a value to the parameter defined in the first column - Affected Parameter. Therefore, its value may change during each evaluation.
  • Notes - not used in computation - simply for reference.

To add a parameter rule to the Simulation, click the upward arrow (G). It will then be added to the table.

To remove a rule, highlight the entry in the table and click the downwards arrow (H).

To modify a rule, click the downwards arrow (H) to move its contents to the lower row (F), perform modifications and then click the upward arrow (G) to return the modified rule to the rules table. When the rule is moved down, the next record is highlighted. The rule will be added just before the highlighted record; i.e., back into the same position unless you choose to modify the highlighted record. The return position of the rule can be changed by highlighting a different record or it can be added at the end of the rules table if no item is highlighted.

6.3 Cost/Quality of Life (QoL) Wizard

The Cost/Quality of Life (QoL) Wizard is designed to make it easy to use Coefficients (see Parameters) to calculate expenses, based on conditions of the population. The cost wizard uses the formulas described in the paper: Zhou H, Isaman DJ, Messinger S, Brown MB, Klein R, Brandle M, Herman WH. A computer simulation model of diabetes progression, quality of life, and cost. Diabetes Care. 2005;28(12):2856-63.

Adding a Coefficient Update Rule

  1. From within the Simulation Project form, click the 'Stage 4 - Update Costs' tab, and then the 'Cost/QoL Wizard' button (I). This button will be visible only when this tab is selected.