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The European Union has seen an increased number of asylum seekers and economic migrants over the past few years. There will be request to assess some of these individuals to see if they have an intellectual disability (ID). If this is to be done using the current internationally recognized definitions of ID, we will need to be confident that the IQ tests we have available are able to accurately measure the IQs of people from developing countries. The literature showing substantial differences in the mean measured IQs of different countries is considered. It is found that, although there are numerous problems with these studies, the overall conclusion that there are substantial differences in mean measured IQ is sound. However, what is not clear is whether there are large differences in true intellectual ability between different countries, how predictive IQ scores are of an individual from a developing country ability to cope, and whether or not an individual's IQ would increase if they go from a developing country to a developed one. Because of these uncertainties, it is suggested that a diagnosis of ID should not be dependent on an IQ cut-off point when assessing people from developing countries.

Background: Previous research with earlier versions of the WISC and WAIS has demonstrated that when administered to people who have intellectual disabilities, the WAIS produced higher IQ scores than the WISC. The aim of this study was to examine whether these differences still exist. A comparison of the Wechsler Adult Intelligence Scale-Third Edition (WAIS-III) with the Wechsler Intelligence Scale for Children-Fourth Edition (WISC-IV) was conducted with individuals who were 16 years old and receiving special education. Materials and Methods: All participants completed the WAIS-III (UK) and WISC-IV (UK). The order of administration was counterbalanced; the mean Full Scale IQ and Index scores on the WAIS-III and WISC-IV were compared. Results: The WAIS-III mean Full Scale IQ was 11.82 points higher than the mean Full Scale IQ score on the WISC-IV. Significant differences were also found between the Verbal Comprehension Index, Perceptual Reasoning/Organization Index and Processing Speed Index on the WAIS-III and WISC-IV, all with the WAIS-III scoring higher. Conclusions: The findings suggest that the WAIS-III produces higher scores than the WISC-IV in people with intellectual disabilities. This has implications for definitions of intellectual disability and suggests that Psychologists should be cautious when interpreting and reporting IQ scores on the WAIS-III and WISC-IV.

Objective: It has been suggested that, as the Wechsler Adult Intelligence Scale-Third Edition (WAIS-III) and the Wechsler Intelligence Scale for Children-Third Edition (WISC-III) give a scaled score of one even if a client scores a raw score of zero, these assessments may have a hidden floor effect at low IQ levels. The study looked for indications of this in a sample of assessments that had been given for clinical and diagnostic reasons. Design: The degree to which a hidden floor effect could be present was assessed by looking at the proportion of scaled scores of one in IQ bands: 50-59, 60-69 and 70 plus and by plotting the distribution of scaled scores in these bands for both the WISC-III and WAIS-III. Method: Fifty WISC-III and 49 WAIS-III assessments were obtained from records and analysed. Results: The distribution of scaled scores in the WAIS-III was approximately normal with very few scale scores of one, suggesting that a hidden floor effect would only be a potential problem for IQs in the 40s and 50s. The WISC-III had a skewed distribution of scaled scores with more scaled scores of one than any other scaled score. Scaled scores of one were shown in all IQ levels up to 70 plus. Conclusions: There is potentially a significant floor effect on the WAIS-III at IQs in the 40s and 50s and on the WISC-III up to IQs in the 70s. There are also indications that the WISC-III has a much harder criterion for gaining a scaled score of two than the WAIS-III, resulting in it producing lower IQs.

The European Union has seen an increased number of asylum seekers and economic migrants over the past few years. There will be request to assess some of these individuals to see if they have an intellectual disability (ID). If this is to be done using the current internationally recognized definitions of ID, we will need to be confident that the IQ tests we have available are able to accurately measure the IQs of people from developing countries. The literature showing substantial differences in the mean measured IQs of different countries is considered. It is found that, although there are numerous problems with these studies, the overall conclusion that there are substantial differences in mean measured IQ is sound. However, what is not clear is whether there are large differences in true intellectual ability between different countries, how predictive IQ scores are of an individual from a developing country ability to cope, and whether or not an individual’s IQ would increase if they go from a developing country to a developed one. Because of these uncertainties, it is suggested that a diagnosis of ID should not be dependent on an IQ cut-off point when assessing people from developing countries. [ABSTRACT FROM AUTHOR]

The accuracy with which current IQ tests appear to be able to categorise people as having a true intellectual ability below 70 depends on the assumptions that are made about how this accuracy should be assessed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The accuracy with which current IQ tests appear to be able to categorise people as having a true intellectual ability below 70 depends on the assumptions that are made about how this accuracy should be assessed. [ABSTRACT FROM AUTHOR]

Seventeen 16-year-olds in special education were given both the Wechsler Adult Intelligence Scale (WAIS)-III and the Wechsler Intelligence Scale for Children (WISC)-IV in counterbalanced order. It was found that there was a significant floor effect on the WISC-IV due to low raw scores and raw scores of 0 being given a scaled score of 1. Extrapolating the relationship between raw scores and scaled scores down below raw score, one showed that the WISC-IV may be overestimating some low intelligence quotients (IQs) by several IQ point due to this floor effect. [ABSTRACT FROM AUTHOR]

Background Previous research with earlier versions of the WISC and WAIS has demonstrated that when administered to people who have intellectual disabilities, the WAIS produced higher IQ scores than the WISC. The aim of this study was to examine whether these differences still exist. A comparison of the Wechsler Adult Intelligence Scale – Third Edition (WAIS-III) with the Wechsler Intelligence Scale for Children – Fourth Edition (WISC-IV) was conducted with individuals who were 16 years old and receiving special education. Materials and Methods All participants completed the WAIS-III (UK) and WISC-IV (UK). The order of administration was counterbalanced; the mean Full Scale IQ and Index scores on the WAIS-III and WISC-IV were compared. Results The WAIS-III mean Full Scale IQ was 11.82 points higher than the mean Full Scale IQ score on the WISC-IV. Significant differences were also found between the Verbal Comprehension Index, Perceptual Reasoning/Organization Index and Processing Speed Index on the WAIS-III and WISC-IV, all with the WAIS-III scoring higher. Conclusions The findings suggest that the WAIS-III produces higher scores than the WISC-IV in people with intellectual disabilities. This has implications for definitions of intellectual disability and suggests that Psychologists should be cautious when interpreting and reporting IQ scores on the WAIS-III and WISC-IV. [ABSTRACT FROM AUTHOR]

The WISC-IV is likely to be in common use for the assessment of children with low intellectual ability for the next 10-12 years. There are several concerns about its uses with these children. Some children may not understand the instructions on some subtests, notably for letter-number sequencing. There may be an unacknowledged floor effect that will result in an overestimate of intellectual ability. The percentile ratings given in the manual are inaccurate for percentiles below 1%. Evidence is presented that the WISC-IV may systematically give lower IQ scores than the WAIS-III when assessing low IQ. [ABSTRACT FROM AUTHOR]

Objective It has been suggested that, as the Wechsler Adult Intelligence Scale-Third Edition (WAIS-III) and the Wechsler Intelligence Scale for Children-Third Edition (WISC-III) give a scaled score of one even if a client scores a raw score of zero, these assessments may have a hidden floor effect at low IQ levels. The study looked for indications of this in a sample of assessments that had been given for clinical and diagnostic reasons. Design The degree to which a hidden floor effect could be present was assessed by looking at the proportion of scaled scores of one in IQ bands: 50–59, 60–69 and 70 plus and by plotting the distribution of scaled scores in these bands for both the WISC-III and WAIS-III. Method Fifty WISC-III and 49 WAIS-III assessments were obtained from records and analysed. Results The distribution of scaled scores in the WAIS-III was approximately normal with very few scale scores of one, suggesting that a hidden floor effect would only be a potential problem for IQs in the 40s and 50s. The WISC-III had a skewed distribution of scaled scores with more scaled scores of one than any other scaled score. Scaled scores of one were shown in all IQ levels up to 70 plus. Conclusions There is potentially a significant floor effect on the WAIS-III at IQs in the 40s and 50s and on the WISC-III up to IQs in the 70s. There are also indications that the WISC-III has a much harder criterion for gaining a scaled score of two than the WAIS-III, resulting in it producing lower IQs. [ABSTRACT FROM AUTHOR]