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8 States

8.1 Overview of States:

States are representations of either discrete stages of a disease or of processes.

8.1.1 State Classifications:

States can be classified according to several types

There must be one Main Process for each model, containing all the other states. The states can be thought of as a tree structure, where a Main Process can contain stages and/or sub-processes, and a sub-process contains states and/or other sub-processes, and so on. During simulation a subject can be in several sub-processes in parallel simultaneously.

The probability for progressing from a state to another during a simulation step is set by the user in Transitions. The probability of staying is a state in a simulation step is one minus the sum of probabilities to progress from that state into the following states.

8.2 Creating States

To set up a new state:

  1. From the main form, click the 'States' button on the left navigation pane.

  2. This form shows all states in the project. To add a new state, press the 'Add' button (A) on the top right of the form, and a new blank row will appear.
  3. Enter the title of the state in the 'Name' box (B).
  4. To define a state of type:

    For a video demonstration on creating states, click here.

  5. If the state is a process/pooling state, meaning that it contains other states, make sure all the "child states" within the process have been created first (repeat from step 2). Next, select a "child state" from the drop-down box (G), and click the up arrow button (I). Repeat for all nested states. Remember, when a child state is a sub-process, all of its children are automatically included.

    It is important to note that the order in which the child states of a sub-process are defined determine the sort order by which transitions are displayed to the user. So they should be defined sequentially. Note that once a sub-process has been referenced, it is difficult to make changes in the system since changes in a referenced sub-processes will be blocked by the system.

    Pooling states are defined for studies that their states combine more than one model state together. The user should define the prevalence of these states. Using the software, pooling states are defined similar to sub-processes with a nonzero prevalence value defined in box (H) before pressing the button (I).

  6. When finished, close the States form to save the states. This will trigger validity checking of the data entered; 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 of creating a process, click here.

8.3 Removing States from a Process

To remove a state from a process:

  1. In the States form, identify the process that you wish to modify.
  2. Highlight the state you wish to remove in the Included States box (F) of that process.
  3. Click the down arrow (J) to remove the state. Note: the state will not be completely deleted, it will only be deleted from the process.

To permanently delete a state:

  1. Remove the state from any processes, using steps above. If the state is itself a process, delete all reference to it from studies that use it as a main process. This may require deletion of other entities and may be difficult if the deletion candidate was extensively used.
  2. In the States form, identify the state that you wish to delete, and click the 'X' (delete) button at the left of that row. This may require deletion of other entities and may be difficult if the deletion candidate was extensively used.

8.4 State Indicator Parameters

Each State or Process has several state indicators associated with it. These state indicators are parameters that are set/reset during a simulation. All state indicators start with the name of the state where spaces are replaced by underscore characters '_'. The type of the state indicator is defined by the suffix at the end of the state name:

Sub-Process state indicators will be set to 1 if the user is in any state / sub-process within this sub-process. This means, for example, that the state indicator of the main process of a model used is simulation is always set to 1. States will generally behave the same with the exception of a simulation step where several sub-processes are joined by a joiner state. In this case, the sub-process indicators will be reset, while the state indicators will remain set until the next simulation step. This behavior allows cost calculations in this simulation step according to the states before the collapsing joiner state was reached.