00:02
Sometimes when people say the epidemiology
of a disease, what they actually mean is the
description of that disease and that brings
us to talking about descriptive epidemiology
or descriptive study, by the way, I don't
like it when we say the epidemiology of a
disease, it's a limiting description of the
full breath and majesty and complexity of
what the science of epidemiology brings to
the table. But when they say descriptive epidemiology,
what we are talking about is the who, who
gets a disease or an outcome, the what, what
is that they're getting, the where, where
is it happening and when, when is it happening.
00:37
Notice that there is no why there, there is
just four W's, who, what, where and when.
00:44
When we're into the why, we're into a deeper
kind of investigation. Descriptive epidemiology
only cares about describing the who, what,
where and when. So let's think of an example.
00:55
Let's decide that we're going to investigate
the prevalence of left-handedness among students
in your neighborhood. Who are we dealing with?
Students. What? Left-handedness. Where? The
place where you live, your neighborhood. And
when? Right now, we care about measuring this
prevalence, this distribution right now and
so the thing that I'm measuring, the thing
that I'm ascertaining is right now 23% of
students in your neighborhood are left-handed.
01:22
That's a very simple and relatively useless
observation, but a good description of descriptive
epidemiology.
01:31
Now I want to talk a bit about the way the
study designs or taxonomise, how we categorize
them. Because a large part of epidemiology
is in designing studies to acquire the evidence
that fits within our research paradigm. So
the first large delineation I want to draw
attention to is qualitative versus quantitative
studies. In qualitative research, that's the
world of social sciences, the world of clinical
science and sometimes health sciences, that's
when we're dealing with descriptions that
are qualitative, words, themes, things like
that. Quantitative research is numbers, statistics
and that's where we're going to live, we're
going to live in the world of quantitative
research in epidemiology. Amongst quantitative
studies we have descriptive versus analytical
studies. Bow descriptive studies we've talked
about already, that's the who, what, where
and when. And one example of a descriptive
study is a cross-sectional study, which we
will describe in greater depth later. I just
did an example, left handedness in my neighborhood,
that's a cross-sectional description of a
particular phenomenon. When we are looking
at two different variables or more variables
and how they relate to one another, then we're
into the world of analysis, into analytical
studies. Now descriptive studies dealt with
one variable really, describing left-handedness.
02:56
Analytical studies are looking at two variables
or more and a relationship between them. Amongst
analytical studies, there are two other categories,
observational or experimental. Amongst observational
studies, there are three perhaps four, large
categories; the case control, the cohort,
the different kinds of cross-sectional studies
and possibly this thing called ecological
study, all of which we learn more about in
another lecture. The distinguishing characteristic
of observational studies is that we observe
them, the universe unfolds and we observe.
03:33
We don't determine who does what or who gets
what, all we do is we watch and we marvel
in the way that the universe unfolds. Experiments
on the other hand, that's when we do get to
interfere a bit. The classical experiment
in epidemiology is the randomized controlled
trial or the RCT, also called clinical trials.
There are other kinds of experiments as well,
there are quasi-experimental designs, there
are natural experiments and we will talk about
more of those in a future lecture as well. Now
when the lay person thinks about an experiment,
they mean any kind of study, any kind of investigation.
When epidemiologists talk about an experiment,
we mean something very particular, we're talking
about when we manipulate a variable. So perhaps
we are deciding who gets a drug versus who
gets a placebo, or who gets to smoke versus
who doesn't smoke. Whenever we are telling
people what to do, we are conducting an experiment.
04:30
We manipulate something, we manipulate a variable.
In observational studies we don't, we let
the universe unfold as it would. We let people
choose what they are going to do. We may select
them, based upon what they're doing, but we
don't tell them what to do. An experiment
involves us changing a variable.
04:46
Well now that we've covered the differences
between analytical and descriptive studies
and the differences between observational
and experiment studies, let's look at some
historical examples. In particular, I want
to talk about the triumphs of epidemiology,
one in particular