which studies we should perhaps give more
weight to because they're probably better.
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.
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.
Now there are different ways of phrasing or
making an evidence pyramid, I like this one.
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.