[Music]
hello and welcome to epidemiology you
know sometimes my clients or my research
partners bring data they've already
collected to me and asked me to analyze
it and the problem is they've arranged
the data or collected in such a way that
it's not really useful or amenable to
easy analysis so today we're going to
learn about data and data analysis and
some of the concepts underlying data so
after today's lecture you're going to
understand the limitations of
quantifying data you're going to be able
to identify the different types of
measurement that a variable can embody
and again variables make up our data
you're going to know why the normal
curve is important in statistics and
you're going to understand the
difference between type 1 and type 2
error also a fundamentally important
concept in statistics and data analysis
so let's begin by asking the question
what is measurement what do you think
measurement is you measure things all
the time you measure your weight you
measure height maybe you measure certain
qualities of a patient's blood sample
measurement is when we assign a quantity
to a quality ultimately there's a
quality we're trying to assess or learn
about and we quantify it in order to do
math on it so a value that may change
then the scope of a problem is a
variable that's what a variable is is
something that's changing all the time
as opposed to a constant there are
causes in life there are variables in
life data analysis is all about
processing the relationship between
variables and constants between each
other so in the world of mathematics a
variable can be written as X it's a
place keeper it's just a registry that
we later fill with a number and perform
functions on in research a variable is a
logical set of attributes like gender or
age something we want to learn about and
in computer science a variable is just a
symbolic name given to an unknown
quantity so the word variable is use in
a variety of contexts depending upon the
discipline that you come from so when
we're defining a variable throughout you
two components to consider there is a
conceptual component and an operational
component
the concept is when we think about the
thing we're trying to measure
conceptually the operational component
is only defined the variable itself and
it's that operational aspect on which
the mathematics is performed so consider
this consider if I'm trying to measure
happiness I devised a scale for
measuring happiness from one to five and
I ask you on a scale of one to five how
happy are you and you say three okay I
can do math on that number now but I've
lost the kind of nuance about the thing
I was trying to measure which is a
happiness that always happens the
variables operational characteristics I
do my statistics on but we can't forget
there's a conceptual underlying
philosophy that's important as well so a
variable is a kind of bucket for
containing quality or information it
isn't the quality or information itself
it's just the container I perform
statistics and mathematics on the bucket
ultimately I want to derive meaning and
philosophy and importance from the
quality inside the bucket there are two
flavors of variables and we've covered
this in a previous lecture but the two
flavors are continuous and categorical
so a continuous variable is something
like age or height or distance or
temperature it's a measurement that has
meaning in between its values I can be
25 years old that can be twenty five
point five years old I can be twenty
five point five one years old there's
still meaning there on the other hand a
categorical or discrete variable doesn't
have meaning in between age group gender
number of children number of siblings
where I was born there's nothing in
between
that gives me meaning those are the two
general categories I can create a
dichotomous categorical variable that
means it has two levels dichotomous
means having two levels like sex male or
female or disease presence yes or no I
can dichotomize an existing continuous
variable in other words I can create a
two level categorical variable from an
existing continuous variable for example
I can take age which is a continuous
flowing concept and create age group out
of it maybe under 18 versus
Keenen over
[Music]