Abnormal psychology is the study of human behavior that differs from the norm in significant ways. The field studies the causes and manifestations of habits, behaviors, thoughts or basic drives that are different from others, and typically, result in significant impairment in life functioning. Clinical psychologists today seek to reduce the value judgments of the past regarding many facets of psychological conditions deemed abnormal. Abnormal technically just means "different from the norm." Clinical psychologists focus on whether or not a person's thoughts and behavior cause distress and social problems. Some abnormal psychological conditions can cause irrational or harmful behavior, either to the self or to others. There are four main criteria used to define abnormality in psychology.
Deviation from the Norm
Statistical criteria can be applied to emotions, thoughts and behaviors. When the intensity of these feelings or behaviors is either significantly higher or lower than the majority of people, the behaviors can be categorized as abnormal. Frequency of behavior and cognition is also important for whether or not a psychological condition meets this criterion. As one example, a person who has an episode of fear and distress upon seeing a spider once, but who is able to overcome this fear easily would be unlikely to be diagnosed with a phobia. Another person who is extremely fearful of spiders and frequently distressed when thinking about them would meet the criteria of frequency and significantly greater than normal fear, thus having a potential phobia.
The functional effect of a person's feelings, behaviors and cognition is another important criterion for defining whether or not a psychological condition is abnormal. If the condition significantly affects a person's ability to care for themselves, have positive relationships, and function well in work or school, it can be classified as abnormal.
Distress and Discomfort
When a psychological condition causes significant personal distress, a third criteria for diagnosis and treatment can be made. Any neurosis, psychosis or cognitive difference such as developmental delay can cause a person to feel very distressed and unhappy. Social discomfort is also a hallmark, such as unhappiness at work, school or at home.
The desirability of a behavior or cognitive difference is the fourth factor used in determining whether or not a psychological condition is abnormal. A genius IQ falls outside the statistical norm, but most people would not say that geniuses are abnormal in a negative way. Individuals with developmental delays are considered to fall under the banner of abnormal psychology, because low cognitive abilities aren't desirable and cause more distress and discomfort than a genius-level IQ.
Some psychologists include varied abnormal categories that recognize that not all abnormal psychological conditions are bad, such as subnormal, supernormal, and paranormal. The Diagnostic and Statistical Manual is currently in its fifth edition, representing a mutually-agreed upon reference and diagnosis book for North American clinical psychologists and other mental health practitioners. In other areas of the world, the ICD-10, used by the World Health Organizations, offers a numerical category and range of disorders that fit under the banner of abnormal psychology.