Another important aspect of emotional development, temperament, has to do with babies' general emotional and social state. Temperament refers to babies' innate personality; the general pattern of how babies will react to and interact with their environment which is present from birth. Two theorists, Thomas and Chess, extensively researched child temperament in the late 1970s. According to their theory, each infant is different and unique in how they react to their environment, and this pattern of reacting is innate, unlearned, and present from birth. As well, every parent is unique in his or her own personality. Often, the goodness of fit, or compatibility, between babies' temperaments and caregivers' own personalities will affect the quality of child - caregiver relationships. Caregivers who educate themselves about how babies' temperaments can affect the relationship between themselves and their babies gain the insight necessary to modify infants' environments so as to better fit their natural temperaments, in the process, making life easier for everyone.
According to Thomas and Chess, there are three general types of temperaments in children: easy, slow-to-warm, and difficult. Easy children are generally happy, active children from birth and adjust easily to new situations and environments. Slow-to-warm children are generally mellow, less active babies from birth, and can have some difficulty adjusting to new situations. Difficult children have irregular habits and biological routines (e.g., eating, sleeping), have difficulty adjusting to new situations, and often express negative moods very intensely. As the category name suggests, these children are the most difficult for caregivers to satisfy and to maintain the energy and joy to care for on a daily basis.
Thomas and Chess identified nine dimensions or qualities that help indicate temperament, including: activity level, rhythmicity, distractibility, approach or withdrawal, adaptability, attention span and persistence, intensity of reaction, threshold of responsiveness, and quality of mood. By looking at these dimensions, caregivers can not only determine what their babies' temperaments are like, but they can also identify ways of interacting and dealing with certain aspects of their temperament in order to foster a nurturing environment for that child and even prevent many complications before they arise.