Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Abnormality is a subjectively defined characteristic, assigned to those with rare or dysfunctional conditions. Defining who is normal or abnormal is a contentious issue in abnormal psychology.
Several conventional criteria
- One criterion for "abnormality" that may appear to apply in the case of abnormal behavior is statistical infrequency. This has an obvious flaw — the extremely intelligent, honest, or happy are just as abnormal as their opposites. Therefore, individual abnormal behaviors are considered to be statistically unusual as well as undesirable. The presence of some form of abnormal behavior is not unusual. About one quarter of people in the United States, for example, are believed to meet criteria for a mental disorder in any given year1. Mental disorders, by definition, involve unusual or statistically abnormal behaviors.
- A more discerning criterion is distress. A person who is displaying a great deal of depression, anxiety, unhappiness, etc. would be thought of as exhibiting abnormal behavior because their own behavior distresses them. Unfortunately, many people are not aware of their own mental state, and while they may benefit from help, they feel no compulsion to receive it.
- Another criterion is morality. This presents many difficulties, because it would be impossible to agree on a single set of morals for the purposes of diagnosis.
- One criterion commonly referenced is maladaptivity. If a person is behaving in ways counter-productive to their own well-being, it is considered maladaptive. Although more tenable than the above criteria, it does have some shortcomings. For example, moral behavior including dissent and abstinence may be considered maladaptive to some.
- Another criterion that has been suggested is that abnormal behavior violates the standards of society. When people do not follow the conventional social and moral rules of their society, the behavior is considered abnormal. However, the magnitude of the violation and how commonly it is violated by others must be taken into consideration.
- Another element of abnormality is that abnormal behavior will cause social discomfort to those who witness such behavior.
- The standard criteria in psychology and psychiatry is that of mental illness or mental disorder. Determination of abnormality is based upon medical diagnosis. This is often criticized for removing control from the 'patient', and being easily manipulated by political or social goals.
- Statistical Infrequency: In this definition of abnormality, behaviors which are seen as statistically rare, are said to be abnormal. For instance one may say that an individual who has an IQ below or above the average level of IQ in society, is abnormal. However this definition obviously has limitations, it fails to recognize the desirability of the particular behavior. Going back to the example, someone who has an IQ level above the normal average wouldn't necessarily be seen as abnormal, rather on the contrary they would be highly regarded for their intelligence. This definition also implies that the presence of abnormal behavior in people should be rare or statistically unusual, which is not the case. Instead, any specific abnormal behavior may be unusual, but it is not unusual for people to exhibit some form of prolonged abnormal behavior at some point in their lives1.
- Deviation from Social Norms defines the departure or deviation of an individual, from society's unwritten rules (norms). For example if one was to witness a man jumping around, nude, on the streets, the man would be perceived as abnormal, as he has broken society's norms about wearing clothing, not to mention ones self dignity. There are also a number of criteria for one to examine before reaching a judgment as to whether someone has deviated from society's norms. The first of these criterion being culture; what may be seen as normal in one culture, may be seen as abnormal in another. The second criterion being the situation & context one is placed in; for example going to the toilet is a normal human act, but going in the middle of a supermarket would be seen as highly abnormal. The third criterion is age; a child at the age of three could get away with taking off its clothing in public, but not a man at the age of twenty. The fourth criterion is gender. The fifth criterion is historical context; standards of normal behavior change in some societies, sometimes very rapidly.
- FF: The Failure to Function Adequately definition of abnormality defines whether or not a behavior is abnormal if it is counter-productive to the individual. The main problem with this definition however is that psychologists cannot agree on the boundaries that define what is 'functioning' and what is 'adequately', as some behaviors that can cause 'failure to function' are not seen as bad i.e. firemen risking their lives to save people in a blazing fire.
- DIM: Deviation from Ideal Mental health defines abnormality by determining if the behavior the individual is displaying is affecting their mental well-being. As with the Failure to Function definition, the boundaries that stipulate what 'ideal mental health' is are not properly defined, and the bigger problem with the definition is that all individuals will at some point in their life deviate from ideal mental health, but it does not mean they are abnormal; i.e., someone who has lost a relative will be distressed, but would not be defined as abnormal for showing that particular behavior. On the contrary, there are some indications that some people require assistance to grieve properly2
A common approach to defining abnormality is a Multi-Criteria approach, where all definitions of abnormality are used to determine whether an individuals behavior is abnormal. For example, if an individual is engaging in a particular behavior that is preventing them from 'functioning', breaks a social norm and is statistically infrequent, then psychologists would be prepared to define this individual's behavior as abnormal. A good example of an abnormal behavior assessed by a multi-criteria approach is depression: it is commonly seen as a deviation from ideal mental stability, it often stops the individual from 'functioning' a normal life, and, although it is a relatively common mental disorder, it is still statistically infrequent; most people will not experience significant major depressive disorder in their lifetime3.
1NIMH factsheet on frequency of mental disorders.
2Article on complicated grief.
3Article on results of the National Comorbidity Study Template:Psychology-stub