Hello, and welcome back to this global health YouTube channel. My name's greg marking
This is the second in a series of videos that we're doing on epidemiology and study design and research methods and in this video
we're going to take the quick look at the difference between case control studies and cohort studies
and we're going to have a look at the the relative strengths of each each study design.
Let's start with case control studies. Now to do a case control study
where you start is with a group of cases, so people that have a particular condition,
they've got a disease and and it's a great study if it's a rare condition or rare disease, right?
So you find people that have a disease let's say, for example,
we found a group of people who at the age of 21 suddenly find their hair goes green.
So we collect those people in a group,
we create an analogous group, right, people that don't have that condition
But are in every other way similar to the first group right then we look back in time,
we look retrospectively at their respective histories and try and identify
exposures that may have -- and we can look at multiple exposures -- that may have led to the condition in this case of green hair and
then we compare these two groups the people with green hair and the people without green hair
and we try to determine if there is a
difference in the extent to which they were exposed to the group of exposures that were interested in.
Okay, so to summarize your case control study: you've got a group of cases and controls. You're looking back in time, so it's
retrospective, you can use rare outcomes right, so you're looking at an outcome
and then looking backwards that's important because when we talk about cohort studies
It's the office [where] run so you're looking at rare outcomes
You're looking backwards in time, so it's retrospective you're talking about looking at multiple exposures, now,
importantly you can do it fast right because you can do the study right now you can you can get data today on
what happened in yesteryear.
And it's cheap, right doesn't cost much money to do interestingly or importantly
the evidence that you get from a case control study is not considered to be strong evidence.
Again now let's talk about cohort studies.
Right and we're going to I want you to understand the difference between these two studies now
remember when we talked about a case control study
we started with outcomes of interest sometimes a rare outcome, and we look back in time at multiple exposures.
The cohort study is exactly the opposite we start off with an exposure of interest [right], so it might be a rare exposure
There's just a few people in the world that have been exposed to something that's unusual.
People that have been to the North Pole, right so we will find that group of people we find an analogous group
we find a second group of
people who are in every other way similar to the first group except they haven't had the exposure of interest like these are people that
haven't been to the North Pole, but in terms of their
demography and their age structures and their
socio-economic strata, et cetera, et cetera, you try and make sure that they pretty much the same because you're going to compare these two groups.
Now you look forwards in time
and you follow this group app right?
you follow the cohort app over time to see
what outcomes emerge over time as a result of that exposure, right?
So just to summarize we're talking about a prospective study you looking at
rare exposures you can examine them for multiple outcomes.
It takes a long time to do because you've got to follow this group app over time
It's expensive, right, so if you run a study like that it costs a lot of money
But what you do [do], what you do get out of it is good strong evidence. So it's stronger
it's considered to be stronger evidence than a case control study, okay. I hope that was useful. I hope you found that helpful.
In the next video we're going to look at randomized control trials and the idea of confounding.
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