The mean is a very poor statistic. Does this statement surprise you? If it does, work through the following exercise.

Study this table of temperatures for 3 U.S. cities.

Maximum Temperature Means (Fahrenheit)

for 1961-1990

January July Yearly Mean Fairbanks, AK -1.6 72.3 36.5 Phoenix, AZ 65.9 105.9 85.9 Honolulu, HI 80.1 87.5 84.4

- The annual maximum temperature mean for Fairbanks, Alaska is 36.5, but it is a balmy 72.3 degrees in July.

- The mean for Phoenix, Arizona is 85.9, yet it is a cool 65.9 in January.

- The mean is a poor predictor in these 2 cities, but in Honolulu, Hawaii the mean of 84.4 is typical of temperatures year round.

It needs a second statistic, the standard deviation, to make sense of these contradictions

this simple, yet powerful statistic.

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