As hinted in the previous post, there are rare situations in which pie charts are acceptable; typically, these charts must show proportions that add up to 100%. If column charts (or line charts) are used instead, readers who aren't careful may assume incorrectly that the columns add up to the whole.
Pie charts show distributions. How should one state the key message of the following pie chart?
I. Type A is the majority.
II. The most frequent type is Type A.
III. Type A is a minority.
IV. Every other type but A form the majority.
I would pick statement II, followed by statement I. Statement I is the only false statement out of the four if one uses a strict definition of "majority" (more than half). If one goes by the spirit rather than the word of the law, statement I does pick up the key message albeit imprecisely. Statement III is a true statement but particularly misleading in the context of this pie chart. For every type is a minority type if we define "minority" as less than half. Statement IV is a tortuous way to define a "majority" where there is none.
Neither III nor IV points to a key feature of the data. It seems ridiculous to even include them. Lets reveal the underlying data.
Last week, a story coursed through the mainstream media, relating to the above projections published by the Census Bureau. (Projections were created for 2050 but mention was made of the fact that the largest racial group would account for less than half the population by 2042.) Here were some of the headlines:
"2042 to see a white minority" (New York Post, 8/14/2008) -- III
"Minorities fixed to become new majority" (Daily Vidette, Illinois State University, 8/20/2008) -- IV
"US set for dramatic change as white America becomes minority by 2042" (Guardian, 8/15/2008) -- III
"...minorities collectively will make up the majority of people in America by 2042..." (Detroit Free Press, 8/21/2008) -- IV
Like I said, statement III is strictly speaking true but by 2042 every race is projected to be a minority. Statement IV is just odd: of course, if one started adding up enough "minority" types, one will eventually attain majority.
Not all is lost, however. The following headlines painted a more vivid image:
"Whites to lose majority status in US by 2042" (Wall Street Journal, 8/14/2008)
"White Americans no longer a majority by 2042" (Associated Press, 8/13/2008)
Elsewhere, a Boston Globe column makes an important observation: that Hispanic whites should probably be grouped with whites rather than Hispanics. Technically, he argued that Hispanic is not a race. From his point of view, the pie chart looks like this: