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July 2, 2010

Implicit Comparison

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The July 1st ChartPorn daily blog post linked to an interesting interactive graphic for economic indicators from the Wall Street Journal, which the author calls "Danger Signs."

The first graph that appears is called Summer Chills. There are two graphs, one for consumer confidence and one for yield on the 10-yr treasury. When I first looked at this, my impression was that the two charts were related. If you carefully read the caption, you can see that they aren't.



I see some issues between the graphs:
  1. The time frames are different. The CCI graph goes from 2007 through June 2010 and it's by month. However, the 10-yr treasury yield is for the current year and it's by day.
  2. The scale on the 10-yr treasury yield graph is not zero-based, which leads to variances between points that are greater than the relative variance.
  3. The reference bands are a bit distracting.
  4. The level of precision on the mark on the 10-yr treasury yield graph is not necessary. Go with two decimals since that's how it's typically reported.
Some things I like:
  1. Highlighting the current period and adding a data label
  2. Chart headers are clear
  3. Fonts used
  4. Line colors stand out, grabbing your attention
Here's how I would represent the data:



The improvements I have made (for each problem noted above):
  1. The time frames are now consistent; they start at January 2007 and go through June 2010. They also are by month only.
  2. The scale on the 10-yr treasury yield graph is now zero-based.
  3. The reference bands have been muted and I've started them at the 2nd range, not at the bottom.
  4. The line for each measure is a different coloring, triggering you to notice they are distinct.
  5. Finally, I added a dual-axis line chart that shows the relationship between the measures.
While the point the author is trying to represent is valid, properly created graphs are essential to tell the true story.

1 comment :

  1. JohnJuly 9, 2010 at 4:40 PM

    Good write up on implicit comparisons. In too many instances the charts drive a point that may not even exist if the were properly constructed. That results in questioning the integrity or the intelligence of the author. Either way it is not a good situation. John

    ReplyDelete

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