What is ID and how is ID diagnosed?
ID is a developmental disability. Each person with ID will have their own strengths and weaknesses and will require lifelong supports of a personalized level, intensity, and duration to optimally engage in their environment.
Clinical judgment plays an important role in all aspects of the determination of ID. As described in more detail in the Manual, a clinician will consider evidence concerning each of the three diagnostic criteria, including any potential sources assessment or measurement error:
Significant limitations in intellectual functioning, which means a full scale IQ standard score of approximately 2 (or more) standard deviations below the mean as measured with an appropriately-normed, standardized test of intelligence.
Significant limitations in adaptive behavior, which means a standard score of approximately 2 (or more) standard deviations below the mean measured with an appropriate and standardized test of adaptive behavior in one or more of the following domains: conceptual, social, or practical skills.
Onset of both of the above limitations during the developmental period, which means that significant limitations in both intellectual functioning and adaptive behavior in the individual have manifested before the age of 22.
As described in more detail in the Manual, all test results must be interpreted within the context of their administration and any potential sources of testing error. In making a determination of ID, evidence in addition to test scores will inform the diagnostician's clinical judgment of the person's overall functioning.
For more information on the diagnosis of ID, consult the AAIDD manual. The "Twenty Questions" document on this page also contains useful information concerning diagnosis, classification, and clinical judgement.