Introduction to bivariate data - Weebly

[Pages:18]INTRODUCTION TO BIVARIATE DATA

WHY TWO VARIABLES INSTEAD OF JUST ONE?

 We

 Let's collect some data.

(except we don't have time, so you will just read about collecting this data)

Image that everyone in class counts the number of text messages they received yesterday.

Then I select a sample of 10 students and actually record their number of messages received. That's one-variable data, so we could make a dotplot or some other kind of graphical display.

 I want to use this data to PREDICT the number of text messages received by the next randomly chosen student.

?

? How the heck do we do that? ? The best number we can use as a predictor is the

mean from the 10 students in our sample ? But that still might not be a very good prediction

Can we make our prediction better? Is there some ? other variable that influences the number of text messages a student might receive?

 How about the number of messages sent?

Could we collect data on messages sent and received, an then use that to make a prediction of the number of messages received based on how many messages were sent?

 This is what we mean by Bivariate (Two Variable) Data. Instead of looking at one variable at a time, we look at two variables that are related. Perhaps one even depends on the other.

We are able to use the value of one of the variables to make a prediction about the other

 Instead of having one axis or scale, we're going to have two axes. The same ones we call "x" ad "y" in algebra

But instead of just having equations like we usually did in algebra, we're going to start with data, which we can display as a scatterplot.

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