Most introductory psychology texts explain in some detail the symptoms and prevalence of mental illness, which many psychology students can use to understand their own mental health. However, there is a significant difference between short-term mood changes and long-term changes in behavior that may indicate mental illness.

Describe how psychologists use specific diagnostic criteria in the diagnosis of mental illness. Explain the difference between changes in behavior when they are temporary (such as distress, irrationality, unpredictability, and unconventionality) and when they are long term and may indicate a mental illness.