When an individual has less common characteristics than most of the population according to statistics
Based on the idea of normal distribution – most people will be statistically average. Anything that is significantly above or below that average is considered abnormal.
e.g. the average iq is 100. 68% of people have an iq between 85-115. only 2% have a score below 70. those individuals are deemed to be statistically abnormal and are eligible to receive a diagnosis of intellectual disability disorder.
Normal and abnormal are defined in terms of mathematical and statistical data specifically the number of times that a quantified behaviour or trait is found
