In a 2021 commentary regarding the most recent official AAIDD intellectual disability definition and classification manual (2021), I raised a concern regarding AAIDD’s position that only a full scale or global IQ score can be used for a Dx of ID. No room was left for clinical judgement for n=1 unique cases. Click here to download and read the complete article. Below is some select text.
“AAIDD's [IQ] Part-Score Position Is at Variance With Other Authoritative Sources”
In AAIDD’s The Death Penalty and Intellectual Disability (Polloway, 2015), both McGrew (2015) and Watson (2015) suggest that [IQ] part scores can be used in special cases. (Note that these two chapters, although published in an AAIDD book, do not necessarily represent the official position of AAIDD.) The limited use of part scores is also described in the 2002 National Research Council book on ID and social security eligibility (see McGrew, 2015; Watson, 2015). The authoritative Diagnostic and Statistical Manual of Mental Disorder—Fifth Edition (DSM-5) manual implies that part scores may be necessary when it states that ‘‘highly discrepant subtest scores may make an overall IQ score invalid'' (American Psychiatric Association, 2013, p. 37). Finally, in the recent APA Handbook of Intellectual and Developmental Disabilities (Glidden, 2021), Floyd et al. (2021) state ‘‘in rare situations in which the repercussions of a false negative diagnostic decision would have undue or irreparable negative impact upon the client, a highly g-loaded part score (see McGrew, 2015a) might be selected to represent intellectual functioning'' (emphasis added; p. 412).
“ In a unique n = 1 high-stakes setting, a psychologist may be ethically obligated to proffer an expert opinion whether the full-scale score is (or is not) the best indicator of general intelligence. There must be room for the judicious use of clinical judgment-based part scores. AAIDD's purple manual complicates rather than elucidates guidance for psychologists and the courts. In high-stakes settings, a psychologist may be hard pressed to explain that their proffered expert opinions are grounded in the AAIDD purple manual, but then explain why they disagree with the ‘‘just say no to part scores'' AAIDD position.”
