Final answer:
The DSM-5 criteria for intellectual disability include significant impairments in both IQ (around 70 or below) and adaptive functioning, present before the age of 18. The severity is assessed based on adaptive functioning, not a specific IQ score.
Step-by-step explanation:
The criteria for the diagnosis of intellectual disability in the DSM-5 is not solely based on an IQ score. Instead, it requires a comprehensive assessment that includes both a low IQ score (approximately two standard deviations below the mean, which would be about 70 for an IQ test with a mean of 100) and significant impairments in adaptive functioning. Additionally, these impairments must be evident during the developmental period, which is before the age of 18 years. It is important to emphasize that the exact threshold for an IQ score is not fixed at a specific number such as 75, and adaptive functioning encompasses a range of skills including social responsibility, personal independence, and practical skills in daily life.
The distinctions made within the intellectual disability category - mild, moderate, severe, and profound - are characterized not by IQ scores but by the individual's adaptive functioning and how much support the individual requires. This reflects the DSM-5's shift in focus from purely quantifiable measures to a broader understanding of how an individual manages in their everyday environment.