Final answer:
The severity of intellectual disability in the DSM-5 is defined by both the degree of adaptive functioning and the score on an intelligence test.
Step-by-step explanation:
In the current DSM-5, the differences in severity of intellectual disability are defined by d) both the degree of adaptive functioning and the score on an intelligence test. According to the American Psychiatric Association, a person could be diagnosed with an intellectual disability if they have a score approximately two standard deviations below the mean (about 70 on a test with a mean of 100) on an intelligence test, major deficits in adaptive functioning, and if these cognitive and adaptive deficits were present before the age of 18. Intellectual disability includes four subtypes: mild, moderate, severe, and profound, and the DSM-5 provides criteria for each subgroup.