A tale on two charts
Olympic tallies

The dog ate the margins

In his column on automated polls versus traditional telephone polls, the Numbers Guy at Wall Street Journal gave us a few entertaining quotes.

"The dog could be answering the questions, " Ann Selzer, a traditional pollster, said of automated polling, which occurs through automated voice messages to voter who record responses.  Also, WSJ cited a prominent textbook which labelled them as "Computerized Response Automated Polls -- insulting acronym intended."

Reader Mark A. brought this to our attention because of the following chart.  He wondered what the point of the vertical axis was. 

Wsj_pollsAside from that cosmetic problem, the biggest issue is the lack of explanation.  Predictive power, pollster-introduced error, methodological error: what are these?  The article itself gives no clues.  To make sense of the chart, readers need to consult Nathan Silver's (excellent) site, fivethirtyeight.com.  (The gory details here.)

By the way, Nathan's site has a variety of nicely produced charts.  (Like this one, readers will need to dig around to collect background information to interpret some of those charts.)

Another improvement is to provide some sense of the variance in the data, either by showing more than the top five pollsters or by showing the range of errors.  Since the average pollster sits on the right edge, it is as if the right half of the chart was clipped.  In the version below, we found most polls hovering around the average, with two egregiously bad.

If we know which polls are automated and which aren't, then color the dots accordingly.


There are bench players on every chart: these are the titles, axes, labels, text and so on.  They provide background information required to interpret the chart.  They may sit in the margins but their value is not to be underestimated.

Don't let the dog eat the marginal information.

Reference: "Press 1 for Obama, 2 for McCain", Wall Street Journal, Aug 1 2008.


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Mark Alves

Kaiser - thanks for answering my question and providing a source for more information. The fivethirtyeight.com site is a fascinating election resource.

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