Dr. Stella Chess and her husband Dr. Alexander Thomas spearheaded the classic New York Longitudinal study in the early 1950s to track hundreds of children over a 30-year period to understand the tendencies that babies are born with and how they influence their lives, and from that research they developed the 9 Temperamental Traits.[i]
The traits are:
5 Chess, Dr. Stella, and Dr. Alexander Thomas. TEMPERAMENT: Theory and Practice. Psychology Press, 1996.