This content introduces two new topics relevant to the AP curriculum: systematic random sampling and the distinction between retrospective and prospective observational studies, building upon previously learned sampling techniques and the definition of observational studies versus experiments.
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so before we can officially finish
chapter four I have a few minor topics
that I want to talk about with you guys
here in this video these two topics are
things that were added to the AP
curriculum after our book was written so
they're not actually in our textbook and
they don't pop up in the homework
problems I give you from the book
neither of these topics is very hard
there's something we need to talk about
though because they do appear on the AP
test and it's also a good chance to
review some of the big things we've
talked about in this unit our first
topic is going to give us a chance to
review all of the nice sampling
techniques that we learned in chapter 4
and these first three options right here
should be pretty familiar to you guys
because we talked about them in quite a
bit of detail as a quick summary right
here SRS a simple random sample every
group of size n so this group of n
people or this group or this group is
equally likely to be chosen it's your
most basic option that if you think
about making a random sample just like
before you took this class you probably
would have been describing an SRS for a
stratified random sample you need to
think of a variable that matters or that
you think will matter and the results
that you get my classic example that I
use a lot is with freshmen sophomores
juniors and seniors so I'd have each
group separate here freshmen sophomores
juniors and seniors each bubble is
different from one another this bubble
is not the same as this bubble right
here etc so you would need to do a
problem where the year in school that
you are would make a difference in how
you would answer a question um so my
classic example is prom and if freshmen
should be able to go freshmen probably
of different opinions than seniors so
what you do then once you establish your
bubbles is you randomly sample some
people out of each of your separate
bubbles and that becomes your sample so
you need to think of a variable that
matters and separate into those groups
before you do your sampling a cluster
sample on the other on the other hand is
when all of your groups are roughly
similar to each other so this group
right here is about the same as this
group right here is about the same as
this group right here I use in apartment buildings
