Amongst many fascinating stories in Malcolm Gladwell's Outliers, chapter eight has one that brings back a strange memory for me. And one that should remind us to always question whether the data we are shown really supports the conclusions we draw from it.

Consider the following table of scores achieved by kids in Baltimore public schools across 1st-5th grade. (The test referred to is the California Achievement Test, but that's not important to the example.)

What conclusions might we draw from this? I think we might reasonably start to think that Baltimore public schools were failing low income pupils. They start off with only a slight disadvantage from their moneyed peers (32 poits), but end school significantly under-performing them (73 points).

... or so it might seem if you take polling results seriously.

In a recent poll, 9% of New Yorkers said they were planning to head to DC for the event. There are about 16 million adults in the New York area, suggesting 1.4 million people planned to make the trip. The lesson here is that there are some things you shouldn't use polling for!

From pollster.com: One problem with a question like this one may be that it lends itself to social desirability bias.

There are some occasions where you need to keep your data gathering quiet!

From the excellent XKCD. 

I also love this one.
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