Patricia Cohen, a researcher who tracked the mental health of a large group of children as they grew to adulthood, detailing the natural history of psychiatric problems and helping to create a framework for future long-term studies, died on July 16 in Marlborough, Mass. She was 81.

Her daughter, Erika Bourne, said the cause was complications of an infection. Dr. Cohen had dementia, Ms. Bourne said.

Dr. Cohen was a midcareer research psychologist at Columbia University when she devised the project that would become her life’s work. In the early 1980s, she and colleagues recruited more than 800 children as young as 9 years old in upstate New York and began to chart their mental health.

At the time, psychiatrists knew little about when mental health problems emerge and how they evolve through development; diagnoses were snapshots in time, blurrier than they are today.