- [Instructor] Hello, and welcome to this video lecture,
which is on Research Design.
We'll be talking about some of the options
that our researchers have.
First of all time, how long, and in what way over time
does the researcher collect data?
And then I wanna walk you through the basics of project
and proposal design.
So when I'm talking about time dimension,
I'm talking about collecting data over time.
There's two main options cross-section,
and then longitudinal,
and a number of options under longitudinal.
And note that as I go through each of these,
that I'm using the notation,
that T is the number of years or number of time periods
that you are collecting data,
and N is the number of subjects.
The first one, and maybe the one
you're most familiar with, is cross-section.
And this is when T equals one that you're collecting data
at one time and one point in time,
it's sort of a snapshot in time.
The survey that we'll be doing in class is cross-section,
but you have many subjects,
so you maybe do a survey and go out
and collect data from a large N number of subjects,
but just one time.
So T equals one, N equals many is cross-section.
The rest of them will be longitudinal
where you don't just collect data one time,
you collect data many times over specific points in time.
And in many cases it can be graphed.
So very often, when we do this,
we look at the time being on the x-axis
and the variable of interest being on the y-axis.
And you can see that
graduation rate here,
it increases real greatly over time
and then sort of flattens out over the last,
looks like 60 years or so.
So one common longitudinal strategy is time series,
and this is where N equals one, but T equals many.
So here, we're looking at one variable,
one phenomenon over time.
So it could be prices over time,
GDP is a very well known one,
inflation, it could be things like graduation rates
at the university, tuition rates at the university,
carbon in the atmosphere, there's many, many options,
but is a single variable,
looking at a single subject like the economy,
but over many years.
Here's the first one where both T and N
are greater than one.
So here, this is a trend study.
So here we're measuring how does a given attitude
or belief change over time.
Usually it involves sampling.
So every time we draw a new sample,
so it might be Vermont residents, UVM students,
small business owners, but the key here
is that we're drawing a different sample every time.
So if we are looking at the Vermont poll
and ask the same question over time,
and here are just some I thought of, gay marriage,
handgun restrictions maybe
what's the most important problem
facing the state.
So again, it's measuring a trend of a variable,
but looking both over time period
and drawing data from many people,
but with a changing sample each time.
So each time we do this such as the Vermont poll,
we have a new sample.
A cohort study is like that except now,
we are drawing from a specific cohort.
So again, T equals many and N is still many,
but we're sampling from a cohort.
And cohort is a group of people
who have something in common.
So it might be the UVM class of 2021,
or it might be people who graduated high school in 1983,
which would be me.
And in a cohort study,
if it was folks who graduated high school '83,
they would draw a new sample each time,
but from that same cohort.
So they would draw a bunch of folks in one year.
And the next year, all of us having in common
that we graduated high school in the same year,
but one year I may be in the sample,
but in the next year, not so.
Again, it's a new sample every time,
but it's drawn from a cohort.
And then there is panel studies.
So here it's T equals many
and N equals many.
But it's the same people over time.
So now we are following the same individual.
So we interview or survey them over time,
or it might be the same business
or the same city
or state or other.
You didn't have analysis,
but we track what they say over time.
So we can actually measure how does an individual person
or an individual city or business change over time,
because we have data that are linked to that individual
over many years.
So just as a review,
you should be able to compare and contrast
these three strategies.
That is the end of part one.
Please go to part two, thank you.