At Harvard, she was supported by a fellowship from the United States Public Health Service (chosen because its application form was short) and because of this ended up working in biostatistics.
After an additional two years as a part-time instructor of epidemiology at Columbia University,[3] she became a regular-rank faculty member in the mathematics department at Hunter College in 1974 and remained there until 1982.
[3][4] In 1983 Wittes moved to the National Heart, Lung, and Blood Institute as chief of the Biostatistics Research Branch, and remained there until 1988,[4] when she left because of a change of employment by her husband,[3] and became a biostatistician for the Department of Veterans Affairs in Connecticut from 1989 to 1990.
[4] Upon the family's return to Washington in 1990, and unable to find a suitable government position, Wittes founded a consulting firm, Statistics Collaborative.
[4] With Michael A. Proschan and K. K. Gordon Lan, she is an author of the book Statistical Monitoring of Clinical Trials: A Unified Approach (Springer, 2006, ISBN 978-0-387-44970-8).