Proportions and Percentages - Communicating Data with Tableau - page 79

Followers of the sport of baseball have long been fascinated with proportions of outcomes
(called stats). As a boy, I would spend all of my weekly allowance on packs of baseball
cards, and each player card would have a table of the player's career stats on the back: games
played, hits, doubles, triples, runs, home runs, batting average. My friends and I memorized
these stats for our favorite players.
Batting average was of particular importance. It was the quintessential metric for efficiency
at the plate. Of all the times a batter came to bat, how often did he get a hit, not including the
times he was walked or hit by a pitch?
NOTE
Batting average is one of the three stats (along with home runs and runs batted in, or RBI)
that together make up the “triple crown” of Major League Baseball batting statistics.
A stat that has recently earned more focus is the “On Base Percentage,” or OBP, in which the
number of times a player gets a hit, walks, or is hit by a pitch is divided by the number of
plate appearances (minus sacrifice hits). It's rarely expressed as a percentage, though. For ex-
ample, Raul Ibanez's OBP in 2012 was 0.308, which is a proportion, not a percentage. A per-
centage would need to be expressed, well, in percent, like 30.8%.
Conveniently, these proportions are already included in the 2012 Yankee player stats table,
so we don't need to create them with calculated fields like we did with the recycle ratios in
Chapter 4 . Let's go ahead and create a simple visualization of the players' batting averages.
To start, we'll drag Name onto the Rows shelf, resulting in a list of all of the players on the
Yankee roster in 2012. Next, we'll drag BA (for batting average) onto the Columns shelf, and
sort in descending order. We'll have a simple bar chart, as shown in Figure 5-1 .