Short Answer: Practically none—but attention tests have other uses.
Longer Answer: Attention tests are very important for discovering what a person can and cannot do. However, for purely diagnostic purposes, cognitive tests of attention should at most play a very limited role, perhaps nudging a diagnostic decision one way or the other in cases that are on the threshold of diagnosis.
There are good reasons to assess cognitive abilities but ADHD diagnosis is not one of them. It is true that people with ADHD are a bit more likely to have certain cognitive profiles than are people without ADHD. For example, people with ADHD, on average, tend to score slightly lower on tests of working memory, processing speed, and verbal fluency than on tests of visual–spatial reasoning, fluid reasoning, and crystallized intelligence (Schwean & Saklofske, 2005). However, most people with ADHD do not have this particular profile and most people with this profile do not have ADHD. In the end, a diagnosis of ADHD cannot be ruled in by any particular cognitive profile, nor can any particular cognitive profile rule it out.
It would be nice if there were a well validated set of attention tests that could identify who has ADHD and who does not. What we need is a set of objectively scored tests of attentional ability on which most people with ADHD score very poorly and most people without ADHD do not score poorly. It would be even better if people with other disorders that affect attention did well on such tests so that the attention deficits measured by the tests would be specific to ADHD.
Sadly, no such battery of tests exists and probably never will. It is not for lack of effort that such a test battery has not been found. Indeed, there is no shortage of tests of attention and there are many studies showing that, on average, people diagnosed with ADHD score somewhat worse on such tests than do people who do not have ADHD. Tests that discriminate between people with ADHD and same-age peers from the population include measures of sustained and divided attention, working memory, verbal fluency, complex information processing speed, response inhibition, and verbal list learning (Schwean & Saklofske, 2005; Woods, Lovejoy, and Ball, 2002). Unfortunately, when we compare people with and without ADHD, the mean performance difference on such tests is only about 0.6 standard deviations (Frazier, Demaree, & Youngstrom, 2004), which means that the distributions of scores in the two groups are mostly overlapping.
Although it is possible for researchers to learn quite a bit about ADHD from small-to-modest mean differences in test performance, attention tests do not improve individual diagnostic accuracy very much (Goldstein & Kennemer, 2009). There are useful formulas (e.g., Elwood, 1993) that can be used with attention test scores such that they can assist clinicians in making ADHD diagnoses. In general, when the base rates of ADHD are high, tests of attention tend to have modest positive predictive power but poor negative predictive power (e.g., Doyle Biederman, Seidman, Weber, & Faraone, 2000). In some settings it might be worth the effort to calculate the positive predictive power and negative predictive power of attention tests, but for most purposes, the following guidelines are suggested:
- If you are already confident (in either direction) about whether ADHD is the correct diagnosis, there are no cognitive test results in the world that should undermine your confidence. However, attention tests might be extremely useful for other purposes.
- If you are leaning toward a certain diagnostic decision and the person’s performance on cognitive tests of attention are consistent with your emerging case conceptualization, your diagnostic decision can be made with more confidence.
- If you are dealing with a complex case and are quite unsure about whether ADHD is the correct diagnosis, administering a battery of attention tests is unlikely to help you make up your mind. However, in the process, you might discover really important information about the person.
Doyle, A.E., Biederman, J., Seidman, L.J.,Weber,W., & Faraone, S.V. (2000). Diagnostic efficiency of neuropsychological test scores for discriminating boys with and without ADHD. Journal of Consulting and Clinical Psychology, 68, 477–488.
Elwood, R. W. (1993). Clinical discriminations and neuropsychological tests: An appeal to Bayes’ theorem. The Clinical Neuropsychologist, 7(2), 224−233.
Frazier, T. W., Demaree, H. A., & Youngstrom, E. (2004). Meta-analysis of intellectual and neuropsychological test performance in Attention Deficit Hyperactivity Disorder. Neuropsychology, 18, 543−555.
Goldstein, S., & Kennemer, K. (2009). Neuropsychological aspects of attention-deficit hyperactivity disorder. In C. R. Reynolds & E. Fletcher-Janzen (Eds.), Handbook of Clinical Child Neuropsychology (3rd ed.; pp. 617−633). New York, NY: Springer.
Grodzinsky, G. M., & Barkley, R. A. (1999). Predictive power of frontal lobe tests in the diagnosis of attention deficit hyperactivity disorder. The Clinical Neuropsychologist, 13(1), 12−21.
Schwean, V. L., & Saklofske, D. H. (2005). Assessment of Attention Deficit Hyperactivity Disorder with the WISC-IV. In A. Prifitera, D. H. Saklofske, & L. G. Weiss (eds.), WISC-IV clinical use and interpretation: Scientist-practitioner perspectives (pp. 235–280). San Diego, CA: Elsevier Academic Press.
Woods, S. P., Lovejoy, D. W. & Ball, J. D. (2002). Neuropsychological characteristics of adults with ADHD: A comprehensive review of initial studies. The Clinical Neuropsychologist, 16(1), 12−34.