Data Viz Done Right

July 14, 2011

Chart abuse: A stacked column chart dissected

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I ran across this chart today on the Chart of the Day blog.  From the article:

“Below is a look at the number of running backs selected in the first round during the Super Bowl era (1967-2010) as well as the number of running backs taken among the top ten picks.”

This stacked column chart needs improvement. Why?

  1. The commentary for the chart is misleading.  It indicates that your comparing the total running backs drafted in the first round to those in the top 10, which would lead you to believe the top 10 is percentage of the total running backs.
  2. How can you tell how many running backs were taken in the top 10?  You have to guess at that number since there’s no vertical axis.
  3. What do the labels on the bars mean?  Do they reference the # of Other 1st Rounders or the Top 10 picks or both?
  4. Stacked bars can make it challenging to compare the bars other than the lowest bar.  In this case, a line chart would be a better way to compare the other 1st rounders, though that would defeat the overall purpose of the chart…to show the total number of 1st round picks by year.

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