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These descriptions of Lashonda, Heather, and Carlos illustrate two important characteristics of their development: All three infants have been remarkably consistent in their patterns of emotional expression. Developmentalists call these individual patterns temperament, the characteristic behavioral and emotional style of the infant.
An individual's temperamental style is deeply rooted in biological inheritance, and as such, temperament suggests considerable stability over time, at least through infancy. However, although a childs temperament tends to be stable, it is also subject to modification by experience, particularly over long periods of time (Bates, 1987).
Much of what we know about temperament comes from the New York Longitudinal Study (Thomas & Chess, 1977; 1984). Researchers followed the behavior of 141 subjects from early infancy into young adulthood. They described the children on 9 scales of temperament: activity level, rhythmicity, adaptability, approachability, threshold, mood, intensity, distractability, and persistence. Presumably, a child's profile on these dimensions describes the childs "inborn" personality or temperament. Although temperament resists change, it does change somewhat over extended periods of time.
Although children showed wide individual differences, the researchers were able to classify most of the children into one of three distinct temperamental types (Thomas & Chess, 1977):
The difficult child withdraws from the unfamiliar, adapts slowly to changes in routine, and is irregular in body function, negative in mood, and high in activity level. Difficult children (about 10% of the children studied) are at-risk for the development of behavior problems (Thomas & Chess, 1977).
The easy child is relaxed when approaching new situations, copes well with changes in routine, is regular in bodily function, and maintains a positive mood and low to moderate intensity (about 40% of the children studied).
The slow-to-warm-up child is inactive, somewhat negative in mood, and does not do well in new situations or respond well to change of routine (about 15% of the children studied).
The remaining 35% of children in Thomas and Chess' sample could not be classified into one of these three categories because they showed consistent or mixed profiles of traits.
Temperament provides a preliminary outline of infant personality, an outline that parents must learn to live with. The extent to which the temperaments of parents match the temperament of the infant is known as "goodness-of-fit". An optimal goodness-of-fit exists where parents accept and nurture the given temperament of their child, thereby minimizing the potential for conflict. Keisha's sensitive interaction with Lashonda in the hospital is an excellent example.
Where the "fit" is less perfect, conflict arises. For instance, the mismatch between Heather's "difficult" temperament and her mother's pattern of low energy and depression is a formula for trouble. When the goodness-of-fit is less than optimal, parents typically attempt to alter their child's temperament, often without much success.
The notion of goodness-of-fit cautions that the match between parents and their childrens temperament is more important than temperament itself in predictive developmental outcome. For example, a temperamentally easy baby in the care of a highly irritable and impulsive parents might be at substantially greater risk than a difficult infant in the care of highly flexible and patient parents.