Janet B. W. Williams (born November 15, 1947) is an American social worker who focuses on the diagnosis and assessment of mental disorders. She is Professor Emerita of Clinical Psychiatric Social Work (in Psychiatry & Neurology) at Columbia University. She was a major force in writing the PHQ-9, a 9-question instrument given to patients in a primary care setting to screen for the presence and severity of depression. Source: Wikipedia (en)