Nominal

A typical example of a nominal variable in psychology is diagnosis. The diagnostic system used by clinical psychologists and psychiatrists assigns numbers to different diagnostic categories (Diagnostic and Statistical Manual of Mental Disorders - IV (DSM-IV), American Psychiatric Association, 1994). These numbers are merely arbitrary "codes" for easy record keeping for hospitals and insurance companies. Let's look at three diagnoses -- Schizophrenia - Disorganized Type (295.1); Major Depressive Disorder - Recurrent (296.3); and Obsessive-Compulsive Disorder (300.3). The graph below shows the prevalence of these disorders in a hospital population.