Abnormal behaviour is defined as behaviour that is considered to be maladaptive or deviant by the social culture in which it occurs. Though disagreement exists regarding which particular behaviour can be classified as abnormal psychologists have defined several criteria for purposes of classification.
Literally, the word 'abnormal' means 'away from the norm' hence, abnormal behaviour is behaviour which departs from the norm. In turn norms can be defined in different ways. One is that the behaviour occurs infrequently (statistical infrequent behaviour). Another is that behaviour deviates from the social norms of acceptable behaviour (social norms). A third is that the behaviour is maladaptive, that it has adverse affects on the individual or on the individual's social group. Lastly, abnormality may be defined based on the subjective feelings of misery, depression, or anxiety of an individual rather than any behaviour one exhibits.
The Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV), is a classification system of abnormal behaviours which aids psychologists and other mental health professionals in diagnosing and treating mental disorders.
DSM-IV includes the major categories of abnormal behaviour which are anxiety disorders, such as obsessive compulsive disorders and phobias; affective disorders, which are disturbances of mood such as depression; schizophrenic disorders, which are characterised by major disturbances in personality and distortion of reality; and various personality disorders.
The inability of leading a normal life is considered a failure to function adequately. Symptoms can be not being able to hold down a job, possibly a drifter or the inability of interacting with people in a social setting with resulting to fits of rage. Psychologists have classified these symptoms into specific behavioural classes: dysfunctional behaviour, personal distress, observer discomfort, unpredictable behaviour and irrational behaviour. The more of these indicators present and the more extreme they are,