Categories of Evidence

In a health-related podcast (or any other health-related media) it’s important to know how solid the evidence is supporting a statement. Why? Well, lots of people make lots of statements and the internet is an echo chamber, so if someone says something that sounds good, lots of other people say it too.

Unfortunately, that adds up to a lot of meaningless junk. For that reason, I want to be clear about my information. Think of a category of evidence like a grade — if the evidence is well proven by numerous high-quality research studies, it might get an A. If it’s really just my clinical experience and hasn’t been researched, it won’t. That doesn’t mean the clinical information isn’t valid, it just means we don’t yet know how far we can trust it. Let’s break it down…

Categories of Evidence

AIf information has A level evidence, it means there are large, top-level research studies as well as clinical evidence behind it. These are systematic reviews or meta-analysis, which is a study compiling and mathematically combining the results of many randomized controlled trials.
BB level evidence means that there are more than one high-quality randomized, placebo-controlled clinical trials, done on humans. More than one well-designed study must be getting the same results.
CC level evidence means one of three things. Either there are more than one smaller or lower quality trials, there is strong clinical evidence (which I personally rank much more highly than many scientists or researchers would, because I’m a clinician), or, there are small studies AND clinical evidence.
DD level evidence means that I have seen repeated clinical success, but there is no research to support that.
EE level evidence means there are in vitro (test-tube or Petrie dish studies, or animal studies, but no human studies and I have no relevant experience with it clinically.
FF level evidence means it’s “common knowledge” on the internet, but there are no studies and I have no personal experience with it.
GI’ve never even heard of this and can’t find it anywhere in research. This is the tin-foil hat of evidence.
The Evidence pyramid I use. It’s a lot like grades, but I’m hoping nobody ever got a G.

There are many things to notice about this categorization of evidence, the first of which being that this is NOT a typical research or academic evidence pyramid, because, in those situations, clinical practice results are too unreliable to be included. In clinical practice, however, they’re the bottom line.

The second is that it is highly focused on my clinical experience. There is a reason for that – I’m a clinician. I have seen so many things happen in my practice repeatedly that don’t have any kind of research around them, but they are reliably true in my clients. That is worth so much to me, and I’ll talk a lot about it, but it still means that other people should approach that evidence with caution. It could be that I’m overlooking some contributing factor or something that would cause the results to be reinterpreted.

For example. If I’m giving all my clients with hypertension lima beans (which I’m not, by the way, but just for an example) and they’re all seeing a drop in their blood pressure, that looks like solid evidence to me. But, what if they were all also enrolling in the same meditation class that had been advertising in my waiting room, and that was the real cause for the improvement? Then, I’m drawing a causal relationship with the lima beans and blood pressure that isn’t there and never will be.

I will try to be as clear and upfront about the level of evidence available for any therapy I’m discussing, but always if you have questions, just ask! You can leave comments, leave voice messages on my Anchor podcast page here, or email me at podcast at

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