What is Effect Size and How Does it Help You Pick a Treatment for ADHD?

Do headlines like this make you a little crazy?

  • Mindfulness shown to be 100% effective for treating ADHD
  • Elimination diet cures ADHD in over 70% of children
  • Stimulants are the first line of treatment for ADHD

The first one came across my desk recently and was full of misinformation (I contacted the editors). Yes, mindfulness is a great treatment for ADHD, but it’s not the magic bullet this headline implies.  The second headline touted poorly done research.  The third is actually true, but then what comes to mind is ‘why?”  and “How much better are stimulants than other treatments?”

So how do you compare the effectiveness of treatments in this environment?  Once you get past faulty research, it turns out that a measure called ‘effect size’ can help you answer your questions.  (Statistical background on effect size here if you are interested in the math.)

Effect size is a measurement tool that tells you how well a certain treatment does at treating specific symptoms.  It’s a set scale that is used across research studies so the effect of one treatment can be compared to the effect of another.  An effect size of 1.0 is considered a ‘robust’ response (vs. a 0 which would be no response at all).  A number less than 1.0 is considered less effective on average, while one above 1.0 more effective.  Stimulant medications in general trials have an effect size of .67 to 1.28 depending upon the medication and dosage used in the trial. Stimulant medications in at least one trial where the dosage was optimized for the individual taking the medication had an effect size of 2.2.  That means that if you are going to take a stimulant medication, you should make sure to work with your doctor to get a dose that works well for you in order to maximize your benefit.  Different medications have different effect sizes, for example, the effect size for Vyvanse in an non-optimized trial was 1.28, while for methylphenidates (Ritalin, Concerta) is .75 while the effect size for Strattera is .44 to .66 depending upon the trial.

This doesn’t mean that Strattera isn’t the right medication for you.  An effect size is the relative likelihood that you’ll respond, but any individual may find they do extremely well on one medication and not on another.  My husband could not tolerate stimulants at all, but Wellbutrin (an anti-depressant) worked very well for him though the effect size for treating ADHD is .34. This was in part due to the fact that his primary target symptom was impulsivity, and Wellbutrin happens to be a good choice for that particular symptom for many.

You can find effect sizes for non-medicinal treatments, if they have been researched as a possible ADHD treatment, too.   You have to be careful, though, because some research (like the Scandinavian studies on elimination diets mentioned above) are poorly constructed and provide false data.  Happily, eventually a meta analysis of the most rigorous, double blind research studies was able to debunk the diet claims.

So what are the effect sizes of different treatments, you might ask?  I’ve got an app for that.  Well, okay, a blog post.  You can find the answer here.