Step 3: Explore the data  Graphs
Click this link to open the data file for a followup study on 40 other students.
Important Note: For convenience, we have defined the number of Facebook friends in terms of "hundreds of friends." So a result of 2.18 means that student indicated 218 friends. The brain density measurement is in "arbitrary units."
With two quantitative variables, the appropriate graph to examine is a scatterplot.

For each observational unit, a dot is placed at the intersection of the density value and the number of Facebook friends value. Our convention is to call this the plot of density vs. friends (y vs. x). Take a screen capture and paste a copy of this graph in your report.
(b) In describing scatterplots, our goal is to describe the association between the two variables. To do so, we focus on three things: direction, strength, and form (but you may want to continue on for now and finish this part later).
 Is the direction of the association as expected by the researchers (clarify what was expected)?
 Would you consider it a strong association? (In other words, does knowing a personâ€™s brain density in this region help you predict the number of Facebook friends?)
 Does the pattern of the association seem reasonably well modeled by a line? (or do you see curvature or some other prominent pattern in the graph?)