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12 Parameters

Parameters are used for various purposes by the system. Parameters can specify covariates that will change during simulation or define a demographic characteristic of a subject. They can define constants and other values that can be reused during simulation. They also can be defined by a user-specified function and then used in subsequent functions as a symbol/shorthand for the user specified function; i.e., they may replace complex mathematical expressions or random generators in multiple functions.

Parameters are classified according to Parameter Types and may have different Parameter Validation Rules and data stored within them as explained below.

12.1 Parameter Types

The following parameter types can be defined by the system.

12.2 Parameter Validation Rules

Parameters can be assigned validation rules to verify that the result of the formula is of the specified type. They do not modify the Parameter in any way. a Validation Rule can be:

When defining a parameter with the validation rule Number, Integer, Expression, Table, the user can define additional validation rule parameters of the type [min, max] that will define bounds for this parameter. For example a user who wishes to define a Boolean parameter, should define an integer with the validation rule parameters of [0,1]. Another example is a user who wishes to define a positive integer should define a parameter of the type integer with the validation rule parameter of [0,Inf]. By default and unless specifically requested otherwise by the user by changing the appropriate system options, validation rules and validation rule parameters are checked during simulation at each step to verify values are within the allowed ranges.

Default validation rules and validation rule parameters are defined by the parameter type as stated above.

12.3 Working with Parameters

Creating Parameters

  1. From the main form, click the 'Parameters' button on the left-hand navigation panel. The following form will appear:



  2. To see all parameters, make sure 'ALL User Accessible' is selected, and press 'OK'. You can also decide to check only the parameter types of interest to view instead seeing all parameters. Then the parameter form will appear:



  3. This form displays the Parameter details. To add a new Parameter, click the 'Add' button (A), and a blank row will appear.
  4. Enter the Parameter name in the box (C).
  5. Pick the Parameter Type from the drop-down (D).
  6. Optionally enter a Formula in the box (E). When this entry is left empty, the user is responsible to assign a value to the parameter elsewhere in the system. An expression defined in the formula defines a substitution expression that will be calculated on the fly, whenever encountered, and may receive different values if it includes a random number generator. The formula is a general expression, yet it is restricted by the parameter type and validation rules.
  7. Optionally Pick a Validation Rule from the drop-down (F), which will verify the output type of the Formula. If you do not pick a validation rule, it will be defined by default by the system according to the parameter type.
  8. Optionally Enter the Validation Rule Parameters in the box (G). A Validation Rule will define the range of values the parameter may have within brackets. If you do not pick a validation rule, it will be defined by default by the system according to the parameter type.
  9. Close the form or move to the next record to save the entry. 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 parameters, click here.

Note that the parameters form can accessed from other forms by double clicking a field that requires a parameter. This allows creating parameters on the fly while working from another form.