Visualizing Relationships - Data Points: Visualization That Means Something - page 180

What relationships to Look For
So far you looked at basic relationships with patterns in time and propor-
tions. You learned about temporal trends, and compared proportions
and percentages to see what's the least and greatest and everything
in between. The next step is to look for relationships between different
variables. As something goes up, does another thing go down, and is it
a causal or correlative relationship? The former is usually quite hard to
prove quantitatively, which makes it even less likely you can prove it with
a graphic. You can, however, easily show correlation, which can lead to a
deeper more exploratory analysis.
You can also take a step back to look at the big picture, or the distribution
of your data. Is it actually spaced out or is it clustered in between? Such
comparisons can lead to stories about citizens of a country or how you
compare to those around you. You can see how different countries com-
pare to one another or general developmental can progress around the
world, which can aid in decisions about where to provide aid.
You can also compare multiple distributions for an even wider view of your
data. How has the makeup of a population changed over time? How has it
stayed the same?
Most important, in the end, when you have all your graphics in front of you,
ask what the results mean. Are they what you expected? Does anything
surprise you?
This might seem abstract and hand-wavy, so now jump right into some
concrete examples on how to look at relationships in your data.
Correlation
Correlation is probably the first thing you think of when you hear about
relationships in data. The second thing is probably causation. Now maybe
you're thinking about the mantra that correlation doesn't equal causa-
tion. The first, correlation, means one thing tends to change a certain way
as another thing changes. For example, the price of milk per gallon and
the price of gasoline per gallon are positively correlated. Both have been
increasing over the years.