00:00
Our story begins in the early 19th century
in London England, when a man named John Snow,
whose name you might have heard of, decided
to investigate a cholera outbreak that was
happening in London at the time. Now back
then, we didn't know a lot about what caused
diseases, there was a few theories, some were
more fantastical than others, but there wasn't
a lot of evidence to support many of the theories.
John Snow's innovation was that he was going
to use maps and numbers to describe the epidemic,
the outbreak, now to us today that seems kind
of rational, kind of boring, kind of everyday,
back then it was revolutionary. So what he
did, was he figured out that back in London
in the 19th century, several neighborhoods
were being served by water pumping stations
and he reasoned that probably cholera was
waterborne and he took the time to figure
out which pumping stations were providing
what water to what neighborhoods. His investigation
led him to conclude that one particular pump,
the Broad Street pump, was likely responsible
for most of the cholera outbreaks in that
city. You can go to London today and actually
visit the Broad Street pump, there is a plaque
there that says, "This is the spot where epidemiology
was born", or something like that. It's quite
fascinating and I encourage you to go if you
can.
01:21
Let's look a little bit at the history of
disease before we continue. Before John Snow
and his brethren made their innovations and
discoveries, it was thought that diseases
were caused by miasma. What's miasma? It's
some kind of fantastical poisonous magical
vapor or mist that would emanate from swamps
of the ground and people would shut their
windows at night so it didn't get into their
houses and cause them to be sick and it had
a foul smell associated with it. Miasma doesn't
really exist, we know that today because we
know that diseases are caused by infectious
agents, microbes, pathogens, bacteria, viruses.
01:59
We know this because around the same time
that John Snow was making his investigations,
the microscope made its first appearance and
we could see these microbes in action. So
it was a revolutionary time.
02:11
Let’s look a little bit at the data that
John Snow collected. He looked at the number
of houses being served by a variety of pumping
companies, the Southwark and Vauxhall Company,
the Lambeth Company and other companies in
London. He saw that each was servicing a different
number of houses and he counted the number
of deaths from cholera experienced by those
neighborhoods. To most people, the number
of deaths alone were sufficient to tell the
story, but that's not where John Snow stopped,
he divided the number of deaths by the number
of houses being served in each neighborhood
and got a quotient, a ratio, a proportion.
02:49
Again, to us today that's an obvious thing
to do, back then it was revolutionary, it
was an innovation and by looking at the quotient,
the proportion, he discovered that majority
of deaths were being caused by one particular
pumping station and he narrowed it down to
one pump, the Broad Street pump and today
that's why we have the science of epidemiology.
03:09
It's the science of using non-medical tools,
mathematics, paper, your mind, your hands,
your feet, to learn something about disease
that otherwise you would not have known. So
today we have different kinds of epidemiologists.
I mentioned that John Snow was a kind of outbreak
investigator, a medical detective of some
kind, most physicians who are epidemiologists
are clinical epidemiologists and they bring
to bear a variety of perspectives, they bring
to bear the choices made by their patients,
the clinical research and practice experience
that they have and also the experiences of
their mentors to make decisions for small
groups of people usually in the clinical environment.
Public health epidemiologists are people like
John Snow, these are the individuals who investigate
outbreaks, who figure out which sandwich at
the picnic gave you diarrhea, who figure out
what's probably causing that outbreak of disease
in that community over there, they are also
the ones who planned the vaccine schedules
for a community. Population epidemiologists
look at large disease trends in a population,
the incidence and prevalence, the risks factors
that cause diseases and so forth, obviously
there is a lot of overlap in all these different
types of epidemiologists and there are newer,
emerging types of epidemiologists today. Epidemiology
is forging partnerships with political science,
with economics, with computer science and
genetics; it's a fast evolving and diversifying
science.
04:37
So before I continue, I want to talk about
how we know what we know, it's important to
understand where our discipline fits into
the science of knowing. We call this paradigms,
paradigms of research, paradigms of knowing.
When we talk about paradigms, we're talking
about how our discipline interacts with the
world that understands knowledge and evidence
and truth. There are several dimensions to
a paradigm and I'll suggest you that there
are three main pillars philosophically of
how to define a paradigm. The first is ontology
and that's how we experience reality. Is reality
defined by my imagination or your imagination,
or is reality defined by some objective
truth of the universe? Then we deal with epistemology,
that's how we acquire and process knowledge.
Do we know about the universe from interrogating
it, from talking to people, from collecting
data? And then we have our methodology, maybe
the ways in which we design our studies, that
determines how we understand the universe.
05:42
The important part about all this is that
paradigms of research allow us to define how
the world works and how we extract knowledge
from it. A psychologist, a political scientist,
an economist, an anthropologist, an epidemiologist
interact with the world a bit differently
and define knowledge a bit differently. We
define the questions that we ask a bit differently
as well, when we look at evidence-based medicine,
we're going to phrase a research question
and the paradigm of knowledge from which we
arise, helps us define the types of questions
that we can ask. Our paradigm of research
also tells us what is publishable and what
isn't, because it defines what constitutes
knowledge, what constitutes proper evidence
and epidemiology is, I hope you will conclude
with me, all about how we rank evidence and
understand truth. In essence a paradigm tells
us how the world is structured and tells us
what determines meaning and significance.
06:41
Epidemiology exists within something we call
the Etiologic paradigm, which is a kind of
positivism and it purports that there exists
external objective truth that we can access
via our methodologies, our science, our study
designs. And we can measure risk factors and
things that cause outcomes, smoking causes
cancer, this behavior will cause this other
kind of outcome, that's the nature of the
epidemiologic etiologic paradigm. I bring
this up because it's important that we remember
that epidemiology and any discipline for that
matter is but one path to knowledge, there
are a variety of paths to knowledge, different
disciplines have their own paths. It is important
that we don't descend into arrogance when
we consider the evidence that we choose to
base our medical decision-making on.