There's a bad stomach bug going around this part of town and I think I might know part of the reason why. Today, my good friends over at Chart of the Day published this pinwheel pie chart and I think the filling might be bad, because the pie sure looks ugly.
Here are some of the problems with this chart:
- IT'S A PIE CHART!
- Colors are re-used, or maybe they are so similar it's hard to tell they're different
- The slices are not in order, making it even hard to look up the values (notice how Microsoft is listed ahead of Peter Thiel and some others)
- The dollar amounts are based on their portion of $100B, yet they total up to $101,350,000,000.
- Correspondingly, the percentages add up to 101.4%. How can you have more than 100% of a total?
To highlight the differences, I created the following charts with Tableau.
What I attempted to do here was show the Stated % Share (gray bar) from the pie chart compared to the "Restated % Share" (black bar). I calculated the Restated % Share with the following formula:
SUM([Stated $ Value])/TOTAL(SUM([Stated $ Value]))
NOTE: A special thank you to Marc Reuter (@tableaujedi) for enlightening the ATUG crowd today with some Jedi magic and for showing how to use the TOTAL function. I had never used it before (and didn't know about it either), but I find it totally awesome! It'll be so useful!
Basically, I'm taking the value stated on the pie chart and dividing it by the total value of the pie chart. This gives you the Restated % Share. The label is the difference between the Restated % Share and the Stated % Share.
The chart on the right represents the % variance number (as identified by the label on the left) multiplied by $100B (the estimated total value of Facebook).
If I were one of these shareholders, I'd be a bit concerned about the math. This isn't chump change! In the end, Chart of the Day may have made a $1.35B miscalculation. Oops!
Download the Tableau workbook here and you will see the original and restated data like this: