Assalam alaikum, and welcome back to another ATP video! This time around we'll be
discussing the different study designs. Here is a little diagram to give you an
overview of some of the important studies. This video will focus on individual based
studies, namely: cross-sectional, cohort, case-control, case reports and case series.
Let's start with cross-sectional studies You might ask yourself why is it called
cross-sectional? Well, it's a cross-section of time, that is to say that at this point
in time there were this many cases, this many complications, this many so on and
so forth. So they would be excellent to use to describe estimates like prevalence for instance!
These types of studies help answer what is happening?
Note that we're not necessarily comparing anything just yet,
we're just seeing how much of it is out there! So it's safe to say that you can't really
establish any causality with this type of study. An example of this type of study would be a group
of researchers trying to find the most common complication of let's say multiple sclerosis.
They just try to describe the prevalence of a certain
condition in those with multiple sclerosis. So cross sectional study is an observational
study done on a population at a point in time and it can help us estimate prevalence.
Now let's move on to cohort and case-control studies.
They're almost always mixed up, and are usually found as distractors in various questions
So instead of trying to explain each one separately let's discuss and
highlight key differences between them It's a lot easier to understand both
studies when you think of them visually. Cohort studies first divide the groups
based on risk factors while case-control studies first divide the groups based on disease status.
If we go back to our timeline remember how a cross-sectional study is a cross-section of time,
while it's slightly different here we're intersecting time at
two different points, as shown here Whenever you go back to a previous
time as you're conducting the study, it is called a retrospective study
and whenever you follow up with participants at a later time as you're conducting the study,
it is called a prospective study. They don't differ much on board
exams but in real-life practice retrospective is more time-efficient,
less costly but it suffers from the fact that you can only trust what has been documented,
or might be facing recall bias, which is simply to depend on a person's own memory to collect data.
For example whether a pregnant lady has had fever in the first three months of her last
pregnancy (I personally wouldn't recall exactly but luckily I can't get pregnant)
Also simply because someone hasn't been documented to be a smoker doesn't mean he isn’t.
It's also very important to recall that certain studies need a certain way to analyze them.
In this case cohort studies are recorded using relative risk, while case-control
studies are reported using odds ratio. Here's a little mnemonic to never forget it: case
control: a o, it goes with odds ratio, which is o r, different letters go with different letters.
Cohort o o, goes with relative risk r r, which are the same letters which go with same letters.
An example of a cohort study would look like this: let's say a study was made to
see whether there was any relationship between smoking and lung cancer.
Participants were divided into two groups based on their smoking status,
and were followed for ten years to see how many from each group would develop lung cancer.
Notice how we first divide the goose by risk factor not by the outcome of interest.
Look for keywords that's just if they're going forward in time, as is the case here,
or backwards in time to figure out whether its prospects of retrospective, respectively.
A case control study would be more fixated on the outcome of interest and
at first divided the participants based on whether they had lung cancer or not.
To summarize, cohort and case-control are observational studies that can help us draw
comparisons between a group based on a risk factor or an outcome of interest.
Finally, let's talk about case reports and case series.
A case report is a detailed report of the symptoms signs diagnosis treatment
and follow-up of an individual patient. It could be because of how rare the symptoms
are for a common disease, or because of how common the symptoms are for a rare disease.
They are usually used to describe an unusual or a novel occurrence.
The important take home message here, is that it is only about one individual.
An example of a case report would be a study that is describing the symptoms,
signs, etc… of a person with an extremely rare disease that caused him to be born
with only one cerebral hemisphere (I made this on top of my head but you get the idea)
A case series can be thought of as similar case reports being lumped together. Instead of making
four separate case reports describing a certain cardiovascular condition you
can lump them into one case series if there's enough similarities between the participants.
That's it for today, short and simple! Let us know if you have any questions
in the comment section below. We hope you benefited from this video!
Consider liking and subscribing, and as always thanks for watching!