A researcher specializing in abnormal psychology wants to know if individuals with Generalized Anxiety Disorder (GAD) have different attention capacities than the general population. She recruits 40 people diagnosed with GAD and 40 people without schizophrenia and records their scores on an attention task. What type of scale is GAD in this example? (Note: she doesn't record the severity of GAD. She just measures if it is present or not.)