Chapter 5. Proportions and Percentages
âBaseball is ninety percent mental and the other half is physical.â
Anyone who wants to master the discipline of communicating data needs to learn how to convey proportions and percentages effectively. We see these types of comparisons every day, from the quarterly sales reports to the sports page box scores to the side panels of cereal boxes. Getting them right is important (unless youâre Yogi Berra).
Recall from Chapter 4 that proportions are ratios expressed as values from 0 to 1âwhere the numerator is a partial amount and the denominator is the totalâand percentages are simply ratios expressed as an amount in each hundred. They are most often used to communicate three different types of comparisons:
Part-to-whole
Current-to-historical
Actual-to-target
Letâs consider each one of these types of comparisons one at a time, starting with part-to-whole.
Part-to-Whole
Just how much of baseball is physical, and how much is mental? If these two aspects of the game are mutually exclusive and collectively exhaustive, they should sum to 100%, right? Yogiâs bogus math in this chapterâs epigraph is funny because itâs different than what we know to expect.
In honor of Yogi, letâs stick with baseball as we consider proportions. In this section, weâll consider the team batting statistics for the 2012 New York Yankees.
Followers of the sport of baseball have long been fascinated with proportions of outcomes (called stats). As ...
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