Evidence Pyramid and Level of Evidence – Critical Thinking and Evidence Based Medicine (EBM)

00:01 There are many ways to create an evidence pyramid, but they all sort of agree on several key features. I want you now to guess about where certain kinds of studies may rank on an evidence pyramid. Where at the very top, we have our best quality evidence, at the bottom we have our least quality evidence, so in vitro test tube research, where do you think that is? To the bottom, it's not every good evidence. How about case series? We already mentioned it's not great evidence, it's somewhere in the middle. Randomized controlled trials we think are among the gold standard, the very best in the world, so you know they're on top. What do you think of animal research? We put it down here. How about systematic reviews and meta-analysis? Well if you guessed on top, you're right, because systematic review made up of randomized controlled trials, is probably better than an individual randomized controlled trial. How about case reports? Well they're up there with case series.

01:03 Cohort and case-controls are observational studies and they're near the top as well, and then we have opinions, and they are near the bottom. Now in practice we tend to like systematic reviews and randomized controlled trials a lot, when pressed we will include some observational studies as well. We almost never go beneath the case control, but sometimes we have to.

01:24 Now there are different ways of phrasing or making an evidence pyramid, I like this one.

01:33 This puts expert opinion at the bottom and systematic reviews and RCTs at the top. Now consider your personal experience, whether you're watching government debates or things in the media, what really wins the day is not randomized controlled trials and it's not systematic reviews, it's actually personal and expert opinion. People's opinions carry a lot of weight in public, but in science, it's the experiments and the systematic reviews of experience that carry weight. So remember, when dealing with policy, we like to invert the pyramid sometimes.