Keith Conners, whose work with hyperactive children established the first standards for diagnosing and treating what is now known as attention deficit hyperactivity disorder, or A.D.H.D. — and who late in life expressed misgivings about how loosely applied that label had become — died on July 5 in Durham, N.C. He was 84.

His wife, Carolyn, said the cause was heart failure.

The field of child psychiatry was itself still young when Dr. Conners joined the faculty of the Johns Hopkins University School of Medicine in the early 1960s as a clinical psychologist. Children with emotional and behavioral problems often got a variety of diagnoses, depending on the clinic, and often ended up being given strong tranquilizers as treatment. Working with Dr. Leon Eisenberg, a prominent child psychiatrist, Dr. Conners focused on a group of youngsters who were chronically restless, hyperactive and sometimes aggressive.

Doctors had recognized this type — “hyperkinesis,” it was called, or “minimal brain dysfunction” — but Dr. Conners combined existing descriptions and, using statistical analysis, focused on the core symptoms.

The 39-item questionnaire he devised, called the Conners Rating Scale, quickly became the worldwide standard for assessing the severity of such problems and measuring improvement. It was later abbreviated to 10 items, giving child psychiatry a scientific foothold and anticipating by more than a decade the kind of checklists that would come to define all psychiatric diagnosis.