Definitions of abnormality- statistical infrequency:
AO1- number of times it is seen, e.g. intellectual disability disorder, most have an IQ between 85 and 115, those under 70 are statistically abnormal and diagnosed
AO3- Strength: real-life application, all assessment of patients with mental disorders includes some comparison to statistical norms. Limitation: unusual characteristics can be positive, e.g. IQs over 130 are considered abnormal but not undesirable and requiring treatment, so it should never be used alone