The Intelligence Quotient (CI or IQ) is a score derived from standardized tests that is used to measure intelligence (or, according to some critics, a type of intelligence).

The IQ of a population of a given age has an average of 100 and a standard deviation of about 15. This means that in a Gaussian distribution, the typical bell shape, 95% of the population must be between 70 and 130 IQs.

As a general rule the IQ of a given population improves decade after decade. On the other hand, as a criticism, different tests to measure the IQ provide results that can have important differences between them.

The general idea was that people affected by autism spectrum disorders (ASD) showed in many cases (up to 75%) intellectual disability, an intelligence quotient below 70 (IQ<70).

Second, boys with ASD were said to have a characteristic profile on IQ tests so that they performed much better on the non-verbal part of the test (“performance”; PIQ) as opposed to the verbal skills test (VIQ). It has even been published that those with more anomalous results in the PIQ/VIQ index coincided with those with greater difficulties in their social life, greater head diameter and greater brain volume.

So to speak, more autism. Third, it was also believed that boys with ASD had a characteristic pattern of peaks and valleys in each part of the IQ tests, and these strengths and weaknesses constitute a summary of the characteristics of autism.

However, data from epidemiological studies on the relationship between intelligence quotient and ASD are scarce and contradictory, making the study by Tony Charman and his group at the London Institute of Education published in 2011 interesting.

Previous studies have shown that approximately 50% of children with ASD have intellectual disabilities (what was formerly called mental retardation and corresponds to an IQ of less than 70).

If the study focused on the classical autism group, with stricter criteria than those of ASDs, the analyses raised that level to 60% and 70%, although the studies conducted (Bertrand et al, 2001; Chakrabarti and Fombonne, 2005) had a relatively small sample (n=42 for Bertrand and his group and n=57 for Chakrabarti and Fombonne).

In another study (Yeargin-Allsopp et al., 2003) conducted with a much larger sample (n=987), 68% had intellectual disabilities. In the study of Charman’s group, the sample is intermediate (n=156) but tighter diagnostic criteria were used, more modern and more standardized tests so that the assessment is more complete and the results presumably more reliable.

The clinical evaluations were carried out on 156 children between the ages of 10 and 14, of whom 81 had classic autism and 75 other ASD disorders. Relative proportions within the population of people with autism were adjusted so that the group could be considered an adequate estimate of the general population with ASD.

In the study of Charman and collaborators it was seen -first result- that the IQ was similar for all the sample of children with ASD, finding similar results in those who had classical autism (67.9 ± 24.0) and those who had another ASD (70.1 ± 24.2).

A second important outcome was the proportion of different levels of disability or intellectual ability. The study found that 55.2% of children with ASD had intellectual disability (IQ<70), of which 39.4% had mild disability (50-69), 8.4% medium disability (35-49), 1.9% severe disability (20-34) and 5.5% profound disability (<20).

Of the children who were outside the disability range (>69) 16.6% of the total sample were below the mid-range (70-84), 25.4% were within the median (85-114) and 2.7% were above the median (>115). Again, the proportions for these groups were similar between those with classic autism and those diagnosed with another type of ASD.

Comparing boys and girls, the average IQ for girls was 61.8 (n=16) and that of boys was greater than 71.7. 78.4% of the girls had intellectual disability (IQ<70) compared to 48.0% of the boys, although by the hair they were not statistically significant differences (c2=3.64, p=0.06).

The low number of girls studied (n=14) meant that the confidence intervals for these analyses were too wide, so this difference should be verified in studies with a greater number of subjects. Everything seems to indicate that girls with ASD have a higher probability of intellectual disability than boys, but the study is not conclusive due to the low sample size.

Of the total sample, 126 children with ASD (61 with childhood autism and 66 with other ASDs) were able to complete 10 subtests, 5 non-verbal (performance) and 5 verbal WISC-III tests.

Differences were not significant for both test groups. Each child was then compared to see those where PIQ>VIQ, PIQ=VIQ and PIQ<VIQ. Subgroups represented 28.3%, 58.8% and 12.9% of the total.

There was also some evidence of a difference between tests comparing IQ in performance tests (PIQ) versus verbal tests (VIQ), as evidenced by the proportion (PIQ/VIQ) but these differences were not associated with a characteristic pattern of symptoms as noted above.

In the tests it was found that the results in the vocabulary and verbal comprehension subtests were poor compared to other non-verbal skills. However, neither the block design nor the Object Assembly test showed strengths as noted above.

The idea that the individuals with the best results in the non-verbal tests had higher levels of affectation in social behaviors could not be demonstrated, generating doubts that it is a real group, that is, that these boys can be separated from the rest of the children with ASD as a defined and different type.

This study sheds light on some discrepancies. The IQ measured with the SPM was 20 points higher than that obtained with the WISC FSIQ. Adaptive skills were significantly lower than IQ in children with ASD and were associated with the severity of the early social deficit and IQ itself.

One conclusion is that although the children had a high IQ and therefore, their academic performance was presumably good, their ability to adapt to the environment was much lower and this meant that even those children with IQ similar to or above the average showed a clear disability.

That is to say, a child with autism fails in the areas of communication and social interaction and this affects in a dramatic way his daily life and particularly in the eucative field, something that can be demonstrated if his capacity of adaptability is evaluated.

In the epidemiological sample used in this study, ASD disorders were less associated with intellectual disability than was traditionally considered.

It confirms other studies that only about half of individuals with ASD have an intellectual disability and less than 20% have a medium or severe disability (IQ<50). There was little evidence of a characteristic IQ profile. Finally, adaptive capacity was significantly affected even for those children whose intelligence was similar to the mean.