Psychotherapy: Does it even work?

I like to say that psychotherapy is the treatment that has been researched the most. There is plenty of scientific data available, and when so much data is available, researchers can begin to summarize that data in what we call a systematic review. In fact, there is so much data that we can not only conduct systematic reviews, we can also conduct reviews of reviews. My goal here is not to describe any of these reviews in detail; instead, I hope to draw on what is consistent from one review to the next and to translate that into terms we can more easily relate to.

Overall, psychotherapy, when compared to the absence of treatment, is said to have an effect size of approximately .80. Of course, unless you are a doctoral level psychologist or a researcher, this probably means as much to you as what most theories in quantum physics mean to me. An effect size is a quantification of the size or magnitude of the effect of an intervention; a simple rule of thumb to understand what an effect size represents is to consider an effect size of .20 as small, of .50 as medium, and of .80 as large. Put simply, psychotherapy has a large effect.

However, the meaning of that statistic is still somehow hard to grasp. A simple solution is to translate that effect size into other more meaningful data. For example, an effect size of .80 means that the person who receives psychotherapy, on average, is better off than 79% of those who don’t receive it. It also means that the success rate of the individuals receiving psychotherapy would be close to 69%, compared to a success rate of slightly over 30% for those who don’t receive psychotherapy. Now this is convincing data.

As I was writing this blog, I must have paused a dozen times to blow my nose. I woke up with a fever, muscle pain … and the list goes on.  So why even bother to get a flu shot? The answer to that is actually quite simple: it does help, and that is why your family physician recommends it, just like most health agencies in Quebec and Canada. One way to show that it helps is to look at a statistic called the number needed to treat (NNT), which is the average number of individuals who need to be treated for one individual to benefit from the intervention. If an intervention is highly effective, then the NNT will be lower.

The Influenza vaccine has an NNT of 12. That is why it is highly recommended and promoted. As for psychotherapy, it has an NNT of 3. Makes you think, doesn’t it?


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