Tables and Polls

Tables are often better than charts, especially with just a few data points. But sometimes a graph is what you need. Here’s an example from the Sunday New York Times magazine of August 6th 2006. It showed American opinions on what to do about Iran.

nyt-table.gif

Quick, what’s the message of the table? That most people thought the US should use diplomacy against Iran? If so, then why show three surveys? There must be some kind of trend here. Wait, why is the timeline going from right to left? OK, there seems to have been a dip in support for military action back in May, or was that a rise in the number of people who don’t think Iran is a threat? But there’s a 4% margin of error, isn’t there? Does that matter?

Let’s try a graphical depiction. To reflect the 4% margin of error (presumably a 95% confidence interval 4 percentile points either side of the reported figure) I used an 8 pt line, where 1 pt = 1 pixel = 1 per cent when I originally constructed the graph in Illustrator.

nyttablelines.gif

I went into the public records and added the poll results for February, which were almost exactly the same as June. For some reason the Times left them out, though they had plenty of room. So was the dip in May significant? Did something happen then that the Times should be telling us about? Who knows?

But before we start over-analysing the data, here are two different polls, both taken in February 2006. Note the difference in responses to essentially the same questions.

nyttablebars.gif

So the biggest differences are caused by pollsters; any supposed “trend” in the Times data is no greater than the difference between two simultaneous polls with slightly different questions. If the media just put a few polls side by side, maybe we’d lose our ill-founded confidence in them.



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