According to thomas and chess, who carried out a large-scale study of infants in the new york longitudinal study, what percentage of children were found to be "slow-to-warm babies"?

According to the Thomas and Chess (1987,1991) study there are three basic types such as temperament: easy, difficult, and slow to warm up. The Easy Child is 40% of infants having positive mood and adapts easily day to day routines in infancy and experiences, new situations etc.,Difficult babies: 10% of infants; adapts slow new experiences, and they react negatively to events. Slow-to-warm-up babies: 15% of infants; adapts somewhat difficult at the beginning stage and they become easier to pickup later time.