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How Useful is Computerized Testing for ADHD?
The recent issue of Child Psychiatry and Human Development (Vol 28, 1998) included an article on the diagnosis of ADHD using "objective" laboratory based measures. Many professionals and parents have been hopeful that a reliable and objective method for diagnosing ADHD can be developed, and this article provides a good opportunity to revisit this issue.
An important concern that many have about the diagnosis of ADHD is that it depends to a large degree on subjective judgments of parents, teachers, and physicians. After all, all children display problems with attention, activity level, and impulsive behavior at some times, so at what point does "typical" childhood behavior become "atypical" and result in a meaningful and accurate diagnosis. (For specific information about diagnostic criteria click here. This situation can be more difficult when parents and teachers see the child in different ways, and parents worry about their child's teacher providing inaccurate or biased observations of their child's behavior.
For such reasons, efforts have been made for many years to develop an "objective" procedure that could be used to diagnose ADHD in a reliable and valid manner. The most promising candidate for this is something called a Continuous Performance Test or CPT for short. The way this test basically works is to have a child sit in front of a computer terminal on which various letters, numbers, and/or symbols are repeatedly displayed. The child is instructed to either respond, or to refrain from responding, depending on what appears on the screen.
Unlike your typical computer game, CPT tests are designed to be extremely repetitive and boring. Doing well requires paying careful attention so that careless and impulsive mistakes are avoided . In theory, by comparing a child's score with the scores that are typically received by a child the same age, one can tell whether the child's ability to carefully attend and refrain from making careless, impulsive mistakes is deficient relative to his or her peers. If it is (i.e. if the child does worse on this task than the vast majority of same age children) than the diagnosis of ADHD might reliably be assigned.
In this study, 20 boys who had been diagnosed with ADHD were compared with 52 boys without ADHD on the CPT. The scores of these two groups of boys were compared to see whether the children with ADHD performed significantly worse on the CPT than the control subjects. As has been found in many other studies using this procedure, as a group, boys with ADHD did worse than control subjects.
Now, does that mean that such a test can be used as a good instrument for diagnosing and individual child? Unfortunately, this is not necessarily the case. To use the CPT to diagnose individual children requires that scores above a certain level are considered to indicate ADHD while scores below this level are "normal". When used in this way, the authors report that boys with ADHD were differentiated from the control subjects with "sensitivity and specificity" above 75%.
The "sensitivity" of a test refers to it's ability to correctly identify individuals with a certain condition. In this case a sensitivity of approximately 75% means that 75% of the boys with ADHD (i.e. 15 of 20) scored above the level that is believed to indicate the presence of ADHD. Five boys (i.e. 25%) scored in the "normal" range.
The "specificity" of a test refers to it's ability to only identify as having the disorder individuals who really do. 100 percent specificity would mean that ONLY children who actually have ADHD achieve scores above a certain level and that children without ADHD NEVER DO. In this case, a specificity of 75% means that 75% of the non ADHD children scored in the normal range. This also means, however, that 25% of children without ADHD (about 14 of 52) did as poorly on the test as a child with ADD is supposed to do.
When looked at in this way, you can see the difficulty with using this test for making diagnoses. If one were to rely on a child's CPT score alone to decide whether he or she had ADHD, as many as 25% of children with ADHD would be misdiagnosed as "normal". An equal percentage of children without ADHD would be mistakenly diagnosed as having this disorder. Obviously, both types of diagnostic errors can create real problems.
It is for this reason that many professionals believe that "objective" measures like the CPT should be used only as "adjunctive" methods for diagnosis. The backbone of a good diagnostic work up remains a thorough and well conducted clinical interview with a child's parents and gathering information from the child's teacher. The value of inter viewing the child him or herself for establishing the presence of ADHD symptoms is debatable - especially for young children who often are not accurate reporters - but can be essential for evaluating whether other conditions (i.e. problems with mood or anxiety) may be present. You can go to for a more complete discussion of suggested evaluation guidelines.
Until objective tests like the CPT can be refined to show much higher levels of sensitivity and specificity they should be used cautiously and judiciously. Sometimes, computers can add an aura of "scientific accuracy" that is really not justified. I have heard of parents paying several hundred dollars for such tests that are then used as the primary basis for diagnosing their child. In my opinion, and the opinion of many mental health professionals, this is a misuse of such tests.
Note: This article originally appeared in Attention Research Update, an online newsletter written by Dr. David Rabiner, a Duke University psychologist and former member of CHADD's Professional Advisory Board. You can learn more about Attention Research Update and sign up for a free subscription at www.helpforadd.com.