Types of studies | AP Statistics | Khan Academy

- [Instructor] In this video,
we're gonna get our bearings

on the different types of studies

you might statistically
analyze or statistical studies.

So first of all, it's
worth differentiating

between an experiment and
an observational study.

I encourage you pause this video

and think about what the difference is,

at least in your head
between an experiment

and an observational.

Observational study.

Well, you might already be
familiar with experiments.

You oftentimes have a hypothesis

that if you do something to one group,

that it might have some type
of statistically significant

impact on them relative to a group

that you did not do it to.

And you would be generally right.

That is the flavor of
what we're talking about

when we're talking about an experiment.

An experiment we're
actively putting people

or things into a control
versus treatment group.

In the treatment group, you put the people

and you usually would want
to randomly select people

into the treatment group.

Maybe it's a new type of medication.

And maybe in the treatment group,

they actually get the medication
while in the control group,

which you would put people into randomly,

whether they're in control or treatment,

here they might get a placebo

where they get a pill that
looks just like the medication,

but it really doesn't do anything.

And then you wait some
time and you can see,

is there a statistically
significant difference

between the treatment group on average

and the control group.

So that's what an experiment does.

It's kind of this act of
sorting and figuring out

whether some type of stimulus
is able to show a difference

while an observational study,

you don't actively put into groups.

Instead, you just collect data

and see if you can have some insights

from that data.

If you can say, okay, the data,
there's a population here,

can I come up with some statistics

that are indicative of the population?

I might just wanna look at averages,

or I might wanna find some
correlations between variables.

But even when we're talking
about an observational study,

there are different types of it,

depending on what type
of data we're looking at,

whether the data is
backward-looking, forward-looking

or it's data that we are
collecting right now,

based on what people
think or say right now.

So if we're thinking about
an observational study

that is looking at past data,

and I could imagine
doing something like this

at Khan Academy,

where we could look at
maybe usage of Khan Academy

over time.

We have these things in our server logs,

and we're able to make
do some analysis there.

Maybe we're able to analyze and say,

on average students are
spending two hours per month

on Khan Academy over in 2019.

That would be past data.

And that type of observational
study would be called

a retrospective study.

Retro for backwards and spective, looking.

So retrospective observational study

would sample past data
in order to come up with

some insights.

Now you can imagine there
might be the other side.

What if we are trying to
observe things into the future?

Well, here you might
take a sample of folks

who you think are
indicative of a population

and you might want to
just track their data.

So you could even consider
that to be future data.

So you pick the group,
the sample ahead of time,

and then you track their data over time.

I'm just gonna try these little arrows

that you're tracking their data,

and then you see what happens.

For example, you might
randomly select hopefully

a random sample of a hundred women,

and you wanna see in the coming year,

how many eggs do they
eat on average per day?

Well, what you would do is
you selected those folks

and then you would track that data

for each of them every day.

And then once you have the data,

you could actually do it
while you're collecting it.

But at the end of the study,

you'll be able to see
what those averages are.

But you can also keep track of it

while you're taking that data.

And you could imagine
what this was called.

Instead of retrospective,
we're now looking forward.

So it is prospective, forward
looking observational study.

Last but not least, some of
y'all are probably thinking,

what about if we're doing something now?

If we go out there and we were
to survey a bunch of people

and say, how many eggs did you eat today?

Or who are you going to vote for?

What might we call that?

It's tempting to call it
something with a prefix

and then spective.

So it all matches,

but it turns out that the
terminology that statisticians

will typically use is a sample survey.

That right now you're gonna
take a hopefully random sample

of individuals from the
population that you care about.

And you are just gonna
serve them right now

and ask them, say some questions

or observe some data about them right now.

So I'll leave you there.

This video is to just
give you a little bit of

the vocabulary and a
little bit of a taxonomy

on the types of studies
that you'll see in general,

which is especially useful to know

when you're exploring
the world of statistics.