Standard Deviations by Gary Smith

Author:Gary Smith [SMITH, GARY]
Language: eng
Format: epub
Tags: SOC027000; PSY032000; MAT029000
ISBN: 9781468310689
Publisher: Overlook
Published: 2014-07-30T16:00:00+00:00

There is a cluster of 5 heads at the end of my little experiment. What happened? Did I face a different direction or sit in a different chair? No. Nothing happened that was special or unusual. When we see a data cluster, we naturally think that something special is going on—that there is a reason that these heads (or tails) are bunched together. But there isn’t. Data clusters appear even in completely random coin flips. If you don’t believe it, flip a coin 10 times. Even though every flip is completely random, there is a 47 percent chance that you will have a cluster of at least 4 heads in a row or 4 tails in a row.

The same is true of the geographic location of randomly dropped bombs. There will inevitably be bomb clusters in some areas and no bombs in other areas. A British statistician named R. D. Clarke analyzed data for an area of South London that had been hit by 537 bombs. He divided the area into 576 squares of 1 square kilometer each, and counted the number of bombs that landed in each square. This was compared to the distribution of bombs that would be expected if 537 bombs were randomly dropped on South London. Table 11.1 shows what he found.

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