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The newBPS Guidance on the Assessment and Diagnosis of Intellectual Disabilities in Adulthoodis reviewed. It is argued that the continued use of IQ cut-off points and the introduction of adaptive behaviour cut-off points is not justified if current research on our ability to measure these two variables is properly considered. The greater emphasis on clinical judgment is welcomed.

The paper considers the effect of error in the measurement of low IQ for research, clinical practice and diagnosis. Test error has most impact on diagnosis of intellectual disability in an individual.

This paper examines how far it is valid to generate a profile of an individual’s cognitive abilities using the WISC-IV or WAIS-III for individuals in the low ability range. Data are presented which demonstrate that the WISC-IV and WAIS-III assessments produce different cognitive profiles, when given to the same 16-year-olds who receive special education. It is suggested that at the low IQ level, subtest and index scores may lack sufficient stability for the WISC-IV or WAIS-III to produce reliable cognitive profiles.

The construct of intellectual disability has developed over centuries and has had different functions at different times; from a concept that was used to describe people from whom society needed protecting from in the late to 19th and early 20th centuries, to one used to describe people who are unable to cope in the current environment. It is now defined in terms of having a measured IQ below a fixed cut off point, usually 70, and a low level of adaptive behaviour also often specified in terms of being below a cut off point. Intellectual Disability demonstrates that neither IQ nor adaptive behaviour can be measured with sufficient accuracy for fixed cut off points to be used and suggests a number of new much more loosely defined constructs of intellectual disability based on clinical judgment.

The WAIS-IV is reviewed for its use in the low IQ range. It has a floor that will elevate low score, does not give accurate percentile ranking and may well systematically measure higher than the WISC-IV.

The term learning disability is currently used in the UK to describe people who require a service due to a low intellectual ability. It is argued that the term is demeaning, confusing and, as currently defined, fails to describe the group of people to whom it is currently applied. It is suggested that a better term for researchers to use would be intellectual disability; however, we should avoid labelling individual services users at all.

Three experiments studied timing in rats on two-valued mixed-FI schedules,\ud with equally probable components, FI S and FI L. When the L/S ratio was\ud greater than 4, two distinct response peaks appeared close to FI S and L, and\ud data could be well-fitted by the sum of 2 Gaussian curves. When the L/S ratio\ud was less than 4, only one response peak was visible, but nonlinear regression\ud usually identified separate sources of behavioral control, by FI S and FI L,\ud although control by FI L dominated. The data were used to test ideas derived\ud from Scalar Expectancy Theory (SET), the Behavioral Theory of Timing\ud (BeT), and Learning to Time (LeT).

There is an agreed international definition of ID (ICD-11, DSM-V, AAIDD): \ud • Significantly low intellectual ability (usually taken as IQ 70 or 75).\ud • Significantly low level of adaptive/social behaviour (often defined as two Standard Deviations below the population mean in the composite measure of in two sub scales).\ud • All occurring before the age of 18 years. \ud \ud But there are some problems with this definition. \ud • It is a condition largely created by definition, with arbitrary IQ and adaptive behaviour cut off scores. \ud • It appears to be the only condition in DSM-V based on test scores. \ud • The tests of IQ and adaptive behaviour are not accurate in low range even when used on the population for which they were standardized. This can lead to misdiagnosis. \ud • The question as to what IQ tests mean when used on groups for which the test was not standardized, has not been adequately address. We do know that different populations have different mean IQs but we don’t know why this is, or what the test results predict, or mean. \ud \ud We need to move to definitions based far more on clinical judgment and less on test scores. For example: An inability to cope with the intellectual demands of ones environment.

Purpose \ud The aim of this paper is to present a theoretical explanation as to why young people score higher on IQ tests than their parents would have done at the same age. \ud \ud Background \ud It is now well established that IQ tests score higher as they get older by about .3 of an IQ point per year for each year since they were standardized. So if the average 20 year old in 1972 was given an IQ test standardized in 2015 they would get a measured IQ of about 87, whereas the average 20 year old today would get a measured IQ of about 100. This is the Flynn effect, for which there are a number of diverse possible explanations but not a definitive one. \ud \ud Methods\ud The literature for the Flynn effect and its possible explanations is considered, including two studies by the current author. \ud \ud Conclusion\ud It is likely that the Flynn effect is the result of a number of independent factors. Although some of the factors may result in a genuine increase in intellectual ability, the bulk of it is probably due to a specific increased ability to do IQ tests. It is suggested that this is because modern society makes more intellectual demands on us, presenting us with more situations that are similar to IQ test items and so effectively allowing us to practise doing IQ tests.

A diagnosis of intellectual disability (ID), mental retardation (MR) or Learning Disabilities (LD) can have a major effect on people’s lives. On the positive side it can provide services, finance, help in schools, and can even prevent the recipient from being executed (Flynn 2006; Flynn 2007; Schalock et al 2007). On the negative side it is may be regarded as a stigmatizing label that an individual may seek to avoid (Baroff 1999). \ud \ud Currently a necessary though not sufficient part of the diagnosis of ID is having an IQ below a specified figure, usually 70, or two standard deviations (SDs) below the norm (American Association on Mental Retardation, 2002; American Psychiatric Association 2000; Department of Health 2001; British Psychological Society 2001). This specification of a specific IQ figure implies that an individual has a “true IQ” that can be measured. \ud \ud If different IQ tests systematically measure either higher or lower than other tests it would raise the question as to which IQ test was providing the best estimate of an individual’s true IQ. In the absence of a test that is clearly an accurate measure of true IQ, the best that could be done would be to decide which of the many IQ tests is likely to be the most accurate, and take that as the “gold standard” assessment against which other assessment should be compared. The Wechsler assessments, the WISC-IV and the WAIS-III should have a good claim to be regarded as the gold standard assessments. However, for these assessments to be accepted as gold standard assessments for the diagnosis of ID, it requires that they should produce equivalent IQ scores in the low ability range. We compared the WISC-IV and WAIS-III on a group of 16-year-olds in special education. Sixteen being the age group at which both assessments can be used.\ud \ud Both the WISC-IV and the WAIS-III were given to seventeen 16-year-olds (9 female and 8 male) attending local special schools in counterbalanced order. The results were as follows: \ud \ud WISC-IV WAIS-III Diff r\ud Mean Full Scale IQ 53.00 64.82 11.82 .93\ud \ud In spite of a very high correlation between the two scales there was a highly significant difference between the mean FS IQ on each scale of nearly 12 points (P

The measurement of Low IQ is subject to far more error than has previously been acknowledged. The five point error that is usually acknowledged only takes into account the internal constancy of the test. When other errors due to changes in assessment conditions, the floor effect, the Flynn Effect and the lack of consistency between test the error is about 18 points.