Introduction to individual differences

Individual differences psychology studies the ways in which individual people differ in their behavior. This is distinguished from other aspects of psychology in that although psychology is ostensibly a study of individuals, modern psychologists invariably study groups. For example, in evaluating the effectiveness of a new therapy, the mean performance of the therapy in one group might be compared to the mean effectiveness of a placebo (or a well-known therapy) in a second, control group. In this context, differences between individuals in their reaction to the experimental and control manipulations are actually treated as errors rather than as interesting phenomena to study. This is because psychological research depends upon statistical controls that are only defined upon groups of people. Individual difference psychologists usually express their interest in individuals while studying groups by seeking dimensions shared by all individuals but upon which individuals differ. Individual differences typically includes the study of intelligence (trait) and IQ and the study of personality.

Individual differences of the emotional type were described by Knight Dunlap, in Habits: Their Making and Unmaking (1932), pp 233-234:


 * The timid person has emotions of embarrassment, dismay, apprehension or fear in situations where normal persons show little emotional effect, or where quite different emotions would be more appropriate.
 * An irritable person may "boil over" in an offensive way or express himself snappishly under stimulation which should be only mildly annoying. On the other hand, he may, for politic reasons, somewhat restrain his outward expressions, but still feel the irritation he does not flagrantly display. The bad-tempered person, however, seldom restrains his expressions of irritation completely.
 * Another type of emotionally maladjusted individual is popularly described as "soft." His sympathy is too easily aroused, and he is an easy prey for clever swindlers. He pities not merely the unfortunate person, but also the deliberate miscreant, and so is an impediment to the maintenance of social order and justice. At the other extreme is the "hard-boiled" man, who is callous to the suffering and misfortune of others and who spares the feelings of no one.
 * Self-pity, unlike the emotional defects above described, is not an exaggeration of a normal habit, but is a trait which is undesirable throughout.... However deserving a man may be of pity from others, he cannot afford to pity himself. The neurotic, from whatever complex of disadvantageous traits he may suffer, is especially prone to self-pity, which confirms and strengthens his neurosis.

Bibliographic Reference
Dunlap, Knight. Habits: Their Making and Unmaking. New York: Liveright Publishing Corporation, Inc. (1932).