See here to have more details about False Positive Rate calculation.

Required condition to run the False Positive Rate algorithm:

• Selected User context must be grouped

If above condition is respected, then follow these steps:

1. Select the User context for which you want to compute the FPR
2. Right-click on the selected context and select Algorithms→Compute False Positive Rate
   • Or, from the main toolbar, select MS Identifications→Context→Algorithms→Compute False Positive Rate
3. A progress bar will appear on the screen
   
4. When process is finished, a dialog message will appear to display the FPR in percentage:
   
5. Result can also be retrieved in the Context properties: