Different Standardized Instruments Produce Different IQ Results: Significant Policy Implications

An interesting and controversial article entitled “Stanford-Binet and WAIS IQ differences and their implications for adults with intellectual disability (aka mental retardation)” by Wayne Silverman et al. was published in Intelligence January 2010 (38, 242-248).  The essence of this research article indicates that the WAIS full scale IQ was higher than the Stanford-Binet Composite IQ with a mean difference of 16.7 points.

 The abstract of this article states: “Stanford-Binet and Wechsler Adult Intelligence Scale (WAIS) IQs were compared for a group of 74 adults with intellectual disability (ID).  In every case, WAIS Full Scale IQ was higher than the Stanford-Binet Composite IQ with a mean difference of 16.7 points.  These differences did not appear to be due to the lower minimum possible score for the Stanford-Binet.  Additional comparisons with other measures suggested that the WAIS might systematically underestimate severity of intellectual impairment.  Implications of these findings are discussed regarding determination of disability status, estimating prevalence of ID, assessing dementia and aging-related cognitive declines, and diagnosis of ID in forensic cases involving a possible death penalty.”

 The article identified four significant public policy implications regarding the discrepancy of the Stanford-Binet and the WAIS IQ testing.  These are summarized briefly here. 

 Disability determinations:  Eligibility for adults with ID for support through the Social Security Administration is demonstrated by: (a) a valid contemporaneously established IQ of 59 or less, (b) a valid IQ between 60 and 70 and another substantial physical or mental impairment, or (c) a valid IQ between 60 and 70 and substantial functional impairments.  Based upon the Stanford-Binet results, 94.6% of the sample in this study would be eligible for benefits on the basis of IQ testing alone (assuming that requirements of age of onset and economic need are also met).  However, using the WAIS only 60.8% of the sample would have qualified without additional evidence of disability.  The authors note: “Results of these two tests are clearly not equivalent for this population, and consensus is needed regarding a preferred ‘gold standard’ for SSA disability determination.”

 Prevalence of ID:  Adults are more often assessed with the WAIS, while school age children more often are assessed using either the Stanford-Binet or WISC.  If the scores for adult assessments tend to be, on average 7.5 points higher, simply because of the predominant use of the WAIS, the overall percentage of adults scoring 70 or below would change from 2.3% to 0.6%.  The authors note:  “[T]he public health significance of ID cannot be addressed effectively unless and until we determine the true size of the affected population and the nature of the associated impairments.”

 Declines with aging:  The authors note “Pre-morbid IQ should influence both selection of appropriate instruments for assessment of performance as well as judgments formed from clinical evaluations, and it is abundantly clear that the sets of Stanford-Binet and WAIS IQs described herein cannot both provide valid indications of performance expectations.”  There is a need to determine how best to use IQ test results to inform diagnoses.

 Death penalty cases:  The Supreme Court ruled, in Atkins v. Virginia (2002), that people with ID convicted of capital crimes are no longer subject to the death penalty.  Evidence of a “true” IQ of 70 or below is required as evidence of ID.  This research indicates that a Stanford-Binet is far more likely to support a diagnosis of ID.  While IQ tests should never be selected based upon expectations of a higher or lower result, psychologists are also charged with knowing which test provides the most valid estimate of true intelligence.

 Research conducted by Dr. Wayne Silverman et al. has indicated that there is a substantial difference in the results of IQ testing between the Stanford-Binet and the WAIS, with the WAIS indicating higher scores than the Stanford-Binet for individuals who have ID.  This research indicates that there can be major public policy implications because IQ testing is used for a number of reasons including disability determination, prevalence of ID, decline with aging, and death penalty cases.  Additionally, there are other public policy indications, such as eligibility criteria for service delivery and school accommodations. 

 More research needs to be conducted regarding IQ testing with persons who have ID.  We need further data to determine whether the Stanford-Binet and WAIS produce similar or different results.  Furthermore, other IQ scales also need to be compared with the Stanford-Binet and WAIS for persons who have ID.  This is an important issue that needs to have careful review and study as the public policy implications are huge

 Robert J. Fletcher, Founder & CEO, NADD

The NIH Public Access Author Manuscript of the Silverman et al. article is available at


NADD and the Future of Dual Diagnosis

Three major NADD initiatives combine to provide the hope and reasonable expectation of improved quality of life for individuals who have intellectual/developmental disabilities and mental illness.  

After almost ten years in development, in 2007 NADD published the DM-ID (Diagnostic Manual-Intellectual Disability: A Textbook of Diagnosis of Mental Disorders in Persons with Intellectual Disability), intended to facilitate more accurate psychiatric diagnoses in people with intellectual/developmental disabilities.  The DM-ID has been widely accepted and is considered the gold standard in our field.  It has facilitated more accurate diagnosis and has raised the diagnostic bar.

The preview issue of Journal of Mental Health Research in Intellectual Disabilities (JMHRID) came out in 2007 with the first official issue in 2008.  JMHRID, published by Taylor & Francis, is the official research journal of NADD.  Its purpose is to both disseminate and to stimulate research concerning individuals with a dual diagnosis.  JMHRID provides a roadmap for evidence-based services and treatments.

For the past several years NADD has been developing an Accreditation and Certification Program (ACP) in Dual Diagnosis which will be rolled out later this year.  The ACP is made up of three separate but interrelated quality assurance programs: a competency-based certification program for direct support professionals; a competency-based certification for clinicians; and accreditation of programs.  The ACP is intended to not only recognize organizations and individuals for the quality of their services, but also to raise the bar for standards in the service delivery system.  In this way, the ACP will act to facilitate the provision of better to individuals with a dual diagnosis. 

While the DM-ID, JMHRID, and the ACP are each a significant milestone in and of itself, and each is a major contribution to the field, I believe that the three, working in concert will have a synergistic effect resulting in better treatment, better services, and improved outcomes for individuals with a dual diagnosis, resulting in improved quality of life for the individuals we serve. 

Robert J. Fletcher, Founder & CEO, NADD

Generic Training vs. Specialized Training

Historically, people are training either in the mental health field or the developmental disability field.  Individuals seeking mental health services are generally served by people training in the mental health field.  These professionals usually have no training in developmental disabilities. Conversely, professionals in the developmental disabilities field do not receive training in mental health issues.  We have developed two separate systems: one in mental health and the other in developmental disabilities.  The training in each of these systems is generally of an adequate level for the target population for which they are designed. 

But what about people with a dual diagnosis of mental illness and developmental disability.  For this population, specialized training for professionals is essential.  We need professionals who are cross-trained in both fields.  Staff who provide mental health services for this population need to know the developmental perspectives associated with psychopathology.  Conducting a mental health assessment requires the knowledge and skills associated with developing a developmental bio-psychosocial model of assessment.  For example, assessment of anxiety disorders may be manifested differently in people with mild-moderate levels of intellectual disability compared to severe-profound levels of intellectual disability.

On the other hand, professionals in the developmental disabilities field need to have at the minimum a baseline understanding of signs and symbols of psychiatric disorders in persons with intellectual disability.  The distinction between what is considered a psychiatric disorder vs. a behavioral problem is a clinical challenge, but one that can be best understood through specialized cross-training.

NADD is committed to providing specialized cross training.  We do this through a variety of methods, including:  annual conference, international conference, teleconferences, books, other training materials, and consultation services.

Robert J. Fletcher, Founder & CEO, NADD

Medical Conditions and Behavioral Problems

Writing in 2005, Ann Poindexter noted, “After forty years of working with individuals with mental retardation/intellectual disability and behavioral/psychiatric problems, I continue to be impressed with the importance of medical issues in the presentation of behavioral symptoms” (p. v).  Although it may not be offering new information to say that physical distress caused by non-psychiatric medical problems can provoke changes in mood and behavior in people with ID, this is a concept that bears repeating.  Often the root of a psychiatric referral of a person with ID will turn out to be an undiagnosed medical condition.  People with ID may lack the verbal ability to communicate their discomfort or distress.  They may even lack the cognitive ability to identify the source of their pain.   Health problems that may cause or worsen behavior problems include ear infections, premenstrual pain, sleep disturbances, allergies, dental pain, seizures, constipation, and urinary tract infections.

Addressing the need to assess for medical factors in the context of a psychiatric assessment, Hurley et al. (2007) write in the DM-ID:

Medical problems are often the source of the chief complaint for the mental health interview for an individual with ID, in contrast with the typical  interview for intellectually normal individuals (who can understand that they have a medical condition that could be associated with a mental disorder, such as chronic pain leading to Depressive Disorder).  For persons with ID, the association of medical condition with mental disorder is not generally understood — not by family, not by direct support professionals, and not by clinicians. (p. 17).

A recent study (Charlot et al., 2011) finds that “individuals with ID admitted for inpatient psychiatric care exhibited high rates of medical problems, and these were associated with duration of inpatient stay.”

Improved assessment and treatment of medical conditions may prevent unnecessary psychiatric referrals and may improve the quality of life of many individuals with ID by relieving their prolonged distress caused by undiagnosed and untreated medical conditions.

Robert J. Fletcher, Founder & CEO, NADD


Charlot, L., Abend, S., Ravin, P.,, Mastis, K, Hunt, A, & Deustch, C. (2011). Non-psychiatric health problems among psychiatric inpatients with intellectual disabilitiese.  Journal of Intellectual Disability Research, 55(2), 119-209.

Hurley, A.D., Levitas, A., Lecavalier, L., & Pary, R.J. (2007). Assessment and diagnostic procedures.  In R. Fletcher, E. Loschen, C. Stavrakaki, & M. First (Eds.), Diagnostic manual – intellectual disability (DM-ID): A textbook of diagnosis of mental disorders in persons with intellectual disability.  Kingston, NY: The NADD Press.

Poindexter, A.R. (2005). Assessing medical issues associated with behavioral/psychiatric problems in persons with intellectual disability.  Kingston, NY: The NADD Press.

Systemic Barriers and Promises for the Future

Despite significant progress over the past decade, there still remain gaps in the service delivery systems for persons who have a dual diagnosis of intellectual disability and mental illness.  As CEO of NADD, it is not uncommon for me to receive a call from a parent concerned about a son or daughter who cannot access mental health out-patient or in-patient services because the individual has an intellectual disability.  This systemic barrier has also been identified in the research NADD has been involved with in several states over the last few years.  This barrier has attitudinal, clinical, legal, as well as public policy implications.  One should not be denied services because of a co-existing disorder.  This is contradictory to the Americans with Disabilities Act (ADA).

NADD has worked very diligently in attempts to alter this situation by facilitating the building of bridges between the mental health and developmental disability service systems.  Although each of these two systems has their own eligibility criteria, funding sources, and regulations, an individual who meets the criteria of both systems should have access to services from both systems at the same time.

We must continue our advocacy efforts as individuals, programs, and organizations to insure that persons who have a dual diagnosis receive the appropriate services that they are entitled to receive.

We invite your thoughts on this issue.

Robert J. Fletcher, Founder & CEO, NADD

Identity and Meaning

Who am I?  This is a question that has been asked by almost all individuals at one point or another.  According to Erikson there are two answers: 1) Who is the person who remains the same within me throughout all of my experiences and 2) What group of humans do I most resemble and fit in with.  For individuals with intellectual disabilities the second part of the answer appears to outweigh the first.  ‘Who am I?  I am the kid from Special Ed.  I am the “retard.”  I am one of the ones that no one will eat lunch with.  I am one of the ones who rode the Special Ed bus and now rides a van.’  This identity of having a “developmental disability” appears to far outweigh any other individual sense of self or social identification for the individuals with intellectual disabilities with whom I have worked. This is a powerful identity that, for many individuals, clearly overshadows any internal sense of sameness.  Positive Identity Development is based on the hypothesis that the development of the individual sense of identity, the resolution of the basic question of “who am I?” in a positive manner that separates the self from the stigma of “disabled person,” becomes the foundation for significant psychological growth.

from Positive Identity Development by Karyn Harvey, Ph.D.

NADD Press, 2009

A new book by Dr. Steven Reiss

Dr.  Reiss has written another outstanding books dealing with dual diagnosis.  The book is entitled Human Needs and Intellectual Disabilities:  Applications for Person Centered Planning, Dual Diagnosis and Crisis Intervention.

Human Needs and Intellectual Disabilities identifies the 12 human needs most relevant to the lives of people with intellectual disabilities, autism and related developmental disabilities.  It includes detailed, practical suggestions for caregivers or parents interested in the happiness, quality of life, and self-determintion of their loved ones or consumers.  The book includes detailed, practical suggestions for reducing episodes of challenging behavior and psychiatric symptoms in people with a dual diagnosis (intellectual disabilities and mental illness).  It shows how to substitute the language of individuality (e.g., “friendly person”) for the language of disability (e.g., “person with disability”).  It also reduces the tendency of planners to confuse their own value system for that of the consumer.  The book includes scholarly reviews of dual diagnosis literature on mental illness, prevalence, and assessment.

For further information, please visit our web site, www.thenadd.org.


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