Alexander Thomas, Stella Chess, Herbert G. Birch, Margaret Hertzig and Sam Korn began the classic New York Longitudinal study in the early 1950s regarding infant temperament (Thomas, Chess & Birch, 1968). The study focused on how temperamental qualities influence adjustment throughout life. Chess, Thomas et al. rated young infants on nine temperament characteristics, each of which, by itself, or with connection to another, affects how well a child fits in at school, with their friends, and at home. Behaviors for each one of these traits are on a continuum. If a child leans towards the high or low end of the scale, it could be a cause for concern. The specific behaviors are: activity level, regularity of sleeping and eating patterns, initial reaction, adaptability, intensity of emotion, mood, distractibility, persistence and attention span, and sensory sensitivity. Redundancies between the categories have been found and a reduced list is normally used by psychologists today.