- [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.