ADHD Studies, Inattentive ADD and Sluggish Cognitive Tempo

ADHD Studies often fail to separate out people with Inattentive ADD and Sluggish Cognitive Tempo from the rest of the study participants. The findings that result from these ADHD studies are difficult or impossible to interpret from an Inattentive ADD standpoint.

ADHD Studies

ADHD studies are difficult to interpret because often the study researchers have not stratified their finding by the type of ADHD and the kind of symptoms that was present in the people who completed the study. When you read the findings of the majority of research performed by ADHD studies you invariably are left with the questions, "Were these kids predominantly inattentive?", "Were these kids sluggish and inattentive?”

Another problem with ADHD research studies is that sometimes the researchers will report that whatever intervention they tried showed an improvement in ADHD symptoms but they do not tell you exactly what the improvements were. So you are left scratching your head as to whether the intervention improved attention, hyperactivity, impulsiveness or all the above.

Inattentive ADD and Sluggish Cognitive Tempo

The most frustrating research studies to read are those that lump everyone with ADHD together as one group and completely disregard the symptoms of Inattentive ADD or Sluggish Cognitive Tempo. The symptoms of these two problems were set next to the symptoms of Hyperactive/Impulsive ADHD (ADHD-HI) are so different that it seems absurd to include research subjects that look so different in the same study.

When researchers take the higher road and separate out the Inattentive ADD from the combined type and the ADHD-HI type, they often do not tease out the findings from the Sluggish Cognitive Tempo subjects vs. the Inattentive ADD without Sluggish Cognitive Tempo subjects.

In science lingo this is called not having an appropriate control group for your study. Without an appropriate control group you cannot say much about what you have discovered from your research intervention. If you had a study where you gave the 'Abracadabra' drug to 100 people with ADHD and 50 of those people were hyperactive and Inattentive and 50 were sluggish and inattentive but you did not separate them out you would have a problem.

Let's say the ’Abracadabra’ drug worsened the attention of 50 of your participants and improved the attention of 50, you would say that the 'Abracadabra' drug was no better than placebo. Had you known that 50% of your population was fundamentally different than the other 50% and separated out the group into the sluggish and the hyperactive, then your findings might be totally different and you would have seen that the 'Abracadabra' intervention actually worked beautifully for the sluggish and only did not work well for the hyperactive type.

Because Inattentive Attention Deficit Disorder and Sluggish Cognitive Tempo are minority conditions in ADHD, that is, the majority of people with ADHD have the combined type of ADHD, there are fewer research studies performed on the Inattentive type symptoms of ADHD.  People with Sluggish Cognitive Tempo symptoms are a minority within a minority and that makes it fare even less well when it comes to having ADHD research studies devoted to it.

I recently read an article on the preparation for the new DSM-5 in Wired Magazine where the primary editor of the American Psychiatric Association's diagnostic manual, the DSM-IV, reported that he felt as though the DSM should be seriously questioned. The methods that the DSM used to classify mental illness were flawed according to Dr, Frances Allen. Dr. Frances felt that diagnosing mental illness based on the cluster of symptoms that were present had created a bunch of mental conditions that were lumped together but perhaps unrelated or that were perhaps not mental illnesses as all. He felt that the DSM-IV had served the pharmaceutical companies well but had served patients poorly.

Many mainstream Neuroscientists now feel that the emerging field of neuro-diagnostic psychiatry, a field that has been written about extensively on Dr. Charles Parker's CorePsych blog, will do away with the DSM-5 and may also do away with the flawed research studies that I mention about. Laboratory, x-ray and other diagnostic measurements will be used to classify individuals with certain conditions and then improvements in these measurements will determine the interventions that perform the best to improve individual conditions.

ADHD Studies, Inattentive ADD and Sluggish Cognitive Tempo

ADHD studies are difficult to interpret. They frequently fail to contain an appropriate control group and can be flawed because people with Inattentive ADD and Sluggish Cognitive tempo are lumped together with people that have hyperactive, impulsive and combined type symptoms. The emerging field of neuro-diagnostic psychiatry will improve the chances that people with Inattentive ADD and SCT are studied appropriately and the chances that interventions targeted specifically for people with ADHD-PI and SCT are discovered.


  1. I don't think the inattentive type or combined type are as different in this matter as you think. A study done in 2011 by Barkley, et al., of adults randomly chosen in the population showed that SCT was nearly as common in the Combined type as it was in the Primarily Inattentive type:

    It's behind a paywall, but I purchased a copy and here's what it had to say on the Combined type:

    "And of those falling in the Combined subset of ADHD, 65% also had SCT."

    It further states in the discussion:

    "Approximately, half (54%) of those participants qualifying for SCT had ADHD, yet nearly half did not. Where overlap existed, it was principally with those subtypes of ADHD having significant inattention. Similarly, approximately half of individuals qualifying for ADHD of any type (46%) also qualified for SCT. The overlap with SCT mainly involved individuals having high symptoms of the ADHD Inattention."

    I think inattentive symptoms quite simply are highly comorbid with SCT, and to exclude those with the Combined subtype from being considered as having SCT may do harm.

    I was diagnosed with the Combined type of ADHD, but I had serious problems with attention as well. As well, I had a slow processing speed as repeatedly tested on the WISC-III (at last time checked my Processing Speed Index was an 80); the school records repeatedly showed that I was socially withdrawn and preoccupied with my own internal thoughts and fantasy. I was slow (but accurate) on the Cancellation task. Moreover, when I try to work on something that is highly engaging and fast-paced, I keep having problems slipping into my thoughts, interfering with my work. I've long had difficulties with self-organization and problem-solving, problems which are specific to SCT as shown in the study linked. It's just I was also hyperactive and impulsive as a child--and today, I have a tendency to get agitated.

    I think that the study shows that excluding the Combined subtype from consideration for a diagnosis of SCT is a hypothesis that has been proven wrong. I predict Barkley will be moving on from this point.

  2. Here's a forum post with another study showing the same thing:

  3. Erika Marie,

    Thanks for your great comment!! I found that study really interesting. I think that current fMRI studies are showing that in people with ADHD and SCT there are brain areas that are not working as optimally as they can and that the areas that cause:

    Slow cognitive processing
    impulsive behavior
    loss of emotional control

    can overlap. A person with ADHD can have SCT and impulsive behavior if those two brain areas are the ones that are causing the majority of their disability.

    The issue of inattentiveness is more complicated as it can be caused by many brain disruptions (including all of the above). I think that the psychiatric community recognized that they could not yet determine how to classify SCT given that the symptoms of SCT may co-occur with other brain issues such as PTSD, depression and ADHD but that it may also occur in the absence of these condition.

    Complicated stuff...

    Thanks again.


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