Do people with ADHD typically underperform on IQ tests? [duplicate]

Question

To me, there seems to be a great disagreement about what IQ is supposed to measure. I have heard about psychologists taking ADHD/depression/other mental illnesses into account when deciding on the final score of an IQ testee; that is, they compensate for it, because those illnesses supposedly make the testee underperform.

Now, that rasies the question: what is IQ? Is it supposed to be your average intellectual ability to function across different environment? Well, if so, ADHD poses issues. ADHD will help in some environments, and in others, it will not. If an IQ test is not representative of all those environments, ADHD patients will have skewed results.

Depression will almost certainly not help you in any environment, so should it really be accounted for? Well, some might say that depression is not an essential feature of your mind, but rather an affliction of it. A bump in the door of a Honda Civic Type R 2012 is not a feature of the model, but rather a feature of the car. In the same way, one might say there is the essence of your mind, and then the state that it is in. That state includes non-essential features like your mood, energy level, sobriety, etc. Some might lump conditions like depression into the non-essential features.

Adult ADHD does not go away though, as far as I'm aware. To say ADHD is a non-essential feature of a mind is to define the essence of a mind in a pretty useless way, given that it'll hold little relevance to actual minds. In contrast, talking about one's mind independently from non-essential factors like mood and sleepiness is definitely of relevance, given that it gives you a view of the mind's average performance.

So, if ADHD is an essential feature of a mind, why account for it in IQ testing? Well, maybe it's an admission of IQ tests' bias for uninteresting environments? Perhaps the average performance of someone with ADHD is likely higher than that which an IQ test would indicate, because IQ questions are typically not that interesting, and thus the performance of people with ADHD suffers disproportionately. At the same time, those same people might be really good at things they are interested in (given ADHD can lead to hyperfocus); thus, given that IQ tests' typically do not reflect the performance of ADHD-patients in those environments, an adjustment to the final score is due to truly give a score of average performance in tasks related to general intelligence?

TL;DR: Why might a psychologist bump ADHD-patients' IQ scores in order to account for ADHD? Is it because the intellectual performance of ADHD-patients varies too greatly across different environments, which exacerbates the inaccuracy from the lack of diversity in IQ tests' representation of different environments?

Answer 1

There are many questions in your post, but I will try to answer the main one:

if ADHD is an essential feature of a mind, why account for it in IQ testing?

An Intelligence quotient (IQ) is "a total score derived from a set of standardised tests or subtests designed to assess human intelligence.". Dixit Wikipedia:

Scores from intelligence tests are estimates of intelligence. Unlike, for example, distance and mass, a concrete measure of intelligence cannot be achieved given the abstract nature of the concept of "intelligence"

The process of estimating this measure must take into account Differential item functioning of specific groups (such as people with ADHD). The corresponding section of the wikipedia page mentions autistic children as an example:

Standard intelligence tests, such as the Stanford–Binet, are often inappropriate for autistic children; the alternative of using developmental or adaptive skills measures are relatively poor measures of intelligence in autistic children, and may have resulted in incorrect claims that a majority of autistic children are of low intelligence

I would say, a practitioner must take into account an ADHD diagnostic the way they would take into account autism and other conditions, when attempting to estimate the relative level of intelligence with subjects within the same social group and age cohort.

ANALOGY

• let's consider first sight and hearing: the ability to see and hear should be independent of the IQ (even though lacking those can limit the amount of stimuli received as a child and delay mental development, yielding a lower IQ), yet those are essential features in taking any kind of test designed for seeing and hearing people, and special measures must be taken when testing people lacking or with alterations (e.g. color blindness) in such features. One can argue that those are physical issues, not "mind ones" (which is itself arguable), so

• let's consider diseases such as the common cold or the flu (or any other disease): those are (hopefully) temporary states rather than a permanent issue, which should not affect the IQ but do affect the taking of any test: the tester can recommend to postpone taking the test to a later date or adjust their interpretation of the test result by taking into account the conditions of the test.

• Let's consider now depression (an example you mention) and motivation (an issue in ADHD people): like sight and hearing, those are orthogonal to the relative mental abilities compared to people with the same age and culture, yet they can affect (the development of the mind and) the process of taking the test, and special measures can be taken when testing people with depression (e.g. taking the test a second time when the symptoms of the depression have faded) or having problems to focus on the test (e.g. dividing the test into several blocks of time).

I hope it helps!