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!
