Statistical Infrequency

a person’s trait, thinking, or behavior is classified as abnormal if it is rare or statistically unusual .
For instance, one may say that an individual with an IQ below or above the average level of IQ in society is abnormal.
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 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 lives.
Strengths (AO3)
This definition can provide an objective way, based on data, to define abnormality if an agreed cut-off point can be identified.
No value judgments are made –Homosexuality was defined as a mental disorder under early versions of the diagnostic criteria used by psychiatrists and would not be seen as ‘wrong’ but merely as less frequent than heterosexuality.

However, this definition fails to distinguish between desirable and undesirable behavior. Statistically speaking, many very gifted individuals could be classified as ‘abnormal’ using this definition. The use of the term ‘abnormal’ in this context would not be appropriate.
Many rare behaviors or characteristics (e.g., left-handedness) have no bearing on normality or abnormality. Some characteristics are regarded as abnormal even though they are quite frequent. Depression may affect 27% of elderly people (NIMH, 2001). This would make it common, but that does not mean it isn’t a problem