Hi Paul,
Please attach a snapshot of sample data, so we can help you better.
How about this?
=Sum(If([Condition]="Yes") Then 1 Else 0)
Yeah, this doesn't say anything about the Count of Incidents from Group One or Two, try it first and then we can update it to include Groups One and Two.
Try that and let us know what happens.
Thanks,
Mahboob Mohammed