Why Do Social Structure and Personality Researchers Study Psychological Distress

Why do social structure and personality researchers study psychological distress rather than psychiatric disorder?

A) Measures of psychological distress are broader in scope than measures of psychiatric disorder and thus better represent people's experiences.
B) Psychological distress is easier to measure and is essentially the same as psychiatric disorder.
C) Psychiatric disorder is something that only psychiatrists, who are medical doctors, can measure.
D) Psychological distress is more stable over time than psychiatric disorder.
E) Research participants are hesitant to answer questions about mental illness.