My brother was tested in 1993 and assigned an IQ of 18.  Not to worry, his true Adaptive Behavior composite Score is in the range of 12-28.  I am so relieved. If this was 1921 and we consulted the American Association of Mental Retardation (AAMR), Mike would have been promoted from Idiot (IQ 0-25) to Imbecile (IQ 26-50), with his higher adaptive scores.  Whew! At least the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM IV (TR)) categorized him as severely to profoundly retarded; marginally better language, but not as good as DSM 5, which replaces retardation with intellectually disabled.
My older brother Michael autistic and has never spoken. His attention span is nil, and he doesn’t seem to recognize other people as independent entities. How in the world can anyone measure his quotient of intelligence, if indeed that has any meaning for him? In DSM IV (TR), there is a category for ‘IQ not testable’. I wonder why Michael was not placed in this category.
The Leiter Scale was revised in 1997 and is now called Leiter-R. Although my brother was tested with an older version of this test, I still have questions regarding his candidacy for such a test.
What is this Leiter Scale?
Referring to the trusty Wikipedia, “Leiter International Performance Scale or simply Leiter scale is an intelligence test in the form of a strict performance scale. It was designed for children and adolescents ages 2 to 18…” 
One of the psychological testing services describes Leiter-R as follows:
“Leiter-R is completely nonverbal. It does not require a spoken or written word from the examiner or the child. The easy game-like administration holds the child’s interest and is easily administered; quickly and objectively scored.” 
Easy to use?
In a review of Leiter-R, one teacher provided an anecdote about her five and a half year old son to whom she administered the test.
“…he was initially very interested in the testing process, but he quickly became frustrated with the lack of verbal communication – as did I! The directions for each subtest must be communicated nonverbally by the examiner and the subject must glean what is wanted from gestures and demonstrations. As the test went on, Nathan used a lot of self-talk to fill the verbal communication void. Because it was so quiet during the testing, I found that any noise at all became a huge distraction to the subject.” 
The teacher also noted that the test was difficult to administer without much training and practice.
I do not have the time or the access, for that matter, to do much more than a cursory literature search for the pros and cons of administering the Leiter Scale to inattentive, low functioning autistic individuals like my brother. However, the following reference shows that this question has not been totally overlooked by the scientific community:
“…there is a general consensus that it is more difficult to make a cognitive assessment of younger, low-functioning, and nonverbal children, given their limited social interaction and communication skills. Many features and behavioral problems can further interfere with the accurate assessment of a young child’s cognitive abilities, including difficulty in holding their attention, overactivity, sensory issues, and poor compliance.” 
This paper proposes that a developmental quotient be used instead of an intelligence quotient and goes on to describe Psychoeducational Profile Revised (PEP-R) as such a tool, useful for assessing children with Pervasive Developmental Disorders (PDD). “The PEP-R offers a developmental approach to the assessment of children with autism or related developmental disorders, and is designed to identify idiosyncratic learning patterns.” 
This seems to be an interesting approach, which I would like to discuss in a future post.
There is no doubt in my mind that Mike was not a candidate for the Leiter Scale or any other test that does not take his very limited attention span into account. I don’t think that it matters that much in his case, since he is so severely disabled.
However, others who have greater potential than my brother, would benefit greatly if they can be tested early in life, with more precision.
 Mike was evaluated with the Leiter International Performance Scale
 According to Vineland II Adaptive Behavior Scale, Survey Interview Form
 Sternberg, Robert J. (2000) Handbook of Intelligence. Cambridge University Press
 Portoghese, C. et. al Leiter-R versus developmental quotient for estimating cognitive function in preschoolers with pervasive developmental disorders Neuropsychiatr Dis Treat. 2010; 6: 337–342. Published online 2010 September 7 PMCID: PMC2938283
 Ibid pg 337