Database Reference
In-Depth Information
Chapter 8. Multiple Quantities
“Correlation does not imply causation.”
—Unknown
So far, we've been creating views that focus on one variable at a time. While focus can be
great, there is a whole world of relationships between multiple variables to explore, under-
stand, and communicate. Finding these relationships can change the world (think carbon di-
oxide and global temperature).
One thing to keep in mind when exploring two or more variables at a time is that “correlation
does not imply causation.” What does this oft-quoted phrase mean? Just because two vari-
ables seem to change together doesn't necessarily mean that one causes the other to change,
or vice versa. A third factor could be causing them both to change, or it may be coincidence
and there may not be any causal relationship at all.
You've probably heard the example of rising ice cream sales and shark attacks. They both
may rise together, but as the college textbook example goes, they're both caused by increas-
ing numbers of people at the beach, which is in turn caused by increasing temperature. It's a
silly example intended to illustrate the point, but there's some truth to it. We're very quick to
assume causal relationships exist when all we really have is evidence of correlation. It's
something to watch out for, but we shouldn't let it derail our exploration altogether, either.
In this chapter, we'll consider a number of ways to explore and communicate multiple quant-
ities in the same individual chart. Later, in
Chapter 12
, we'll tackle dashboards, where many
different charts can be added to the same view.
Scatterplots
I'll come right out and say it: I love scatterplots. I love them because they create a two-di-
mensional plane in which a whole host of comparisons can be made in an instant. It's almost
effortless to spot groups of points and individual points that stand apart from the rest, or out-
liers. The first visualization I created with Tableau Public was a scatterplot of the top 100 ca-
reer points leaders in professional hockey history, shown in
Figure 8-1
.
