Political reporters and commentators: It is NOT a “statistical dead heat”!!!

Question:  How often do political reporters and commentators report poll results like

Douche: 52%

Turd: 48%

Margin of Error: + or – 2

(names courtesy of the cartoon South Park) as a “statistical dead heat” between the candidates?

Answer:  All the time!

Problem:  It’s wrong!

So, on the eve of the Arizona and Michigan primaries, here’s my attempt to get political reporters and commentators to get it right tomorrow…

What the “Margin of Error” Really Means:  The “margin of error” is NOT a “window” within which the actual results are equally likely to fall.  So, in the example above, it’s NOT equally likely that Douche and Turd truly both have 50% support.

The margin of error is what we call a “confidence interval,” and it’s generally a 95% confidence interval.  In the example above, this means there’s a 95% chance that Douche’s true support within the polled population (e.g. “likely voters”) is between 50% and 54%, and there’s a 95% chance that Turd’s true support is between 46% and 50%.

So, in the example above, there’s really only a 5% chance that Douche’s true support is below 50%, and there’s really only a 5% chance that Turd’s true support is above 50%.  Conversely, there’s really a 95% chance that Douche’s true support is above 50%, and there’s really a 95% chance that Turd’s support is below 50%.

Bottom line:  In the example above, there’s actually a 95% chance that Douche is winning — it’s NOT a “statistical dead heat”!!!

(If you’re interested in reading more about how often statistics are misinterpreted and misreported, you might like Super Crunchers: Why Thinking-by-Numbers Is the New Way to Be Smart by Ian Ayres, 2007, which explains inaccurate opinion-poll interpretations better than I just did.)

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