Performing sensitivity analysis

To perform sensitivity analysis

1. Build the model and assign constants to the Converters and constant initial values to the Stocks whose values you want to manipulate over a series of sensitivity runs.

2. From the Run menu, choose Sensi Specs.

   The Sensitivity Specs dialog box opens.

3. Select either All combinations or Specific number of runs based on your needs. All combinations is normally used only when all your distribution choices will be Incremental or Ad-Hoc. If you select Specific number of runs enter the number, or use the default of 5. When All combinations is selected each variable will have a number of runs specified and the total number of runs will be the product over all variables.

4. Select the variables you want to control for the sensitivity runs. Add an entry by clicking on the button then choose.

   Tell me how

   Choose a variable in one of the following ways:

   • In the Variable box, begin typing the name of the variable you want to add. A list of matching variables appears. Click the variable you want, (or arrow to it) and press Enter.
   • Using the Variable list at the left of the dialog find the name you want (type part of it to filter the list). Drag the entity you want to the Variable box.
   1. Select a distribution from the dropdown. The fields to be filled in will depend on your selection. For more information about selecting these options, see Selecting sensitivity analysis distributions.
      1. For random distributions you can fill in the seed and distribution parameters. The distribution parameters are the same as those for the Builtins as described in Statistical builtins. If you selected All combinations in step 3 above enter the number of runs.
      2. For the Ad-Hoc distribution enter a comma separated list of numbers to be used.
      3. For Incremental enter the starting and ending values. If you have selected All combination in step 3 above then you can also specify the number of runs to be made.
5. Repeat step 4 for each variable you want.

6. Make sure that the Sensitivity On check box is selected.

   Tip:You need to create comparative graphs and tables to view results for desired variables before you do the sensitivity run.

7. To run sensitivity select S-Run from the Run menu or click on the run button in the bottom right corner. To return to regular runs you need reopen the Sensitivity Specs dialog and uncheck Sensitivity On.
8. After a sensitivity run if you click on the ? at the bottom of comparative graphs or top of comparative tables it will display the sensitivity values used in each of the runs listed.

See Also