future. The standard deviation describes how likely a certain amount of variation (or deviation) is to happen. For example, the average woman in the United States is 5 feet 4 inches tall,128 with a standard deviation of just under three inches. This means that 68 percent of women are between 5 feet 1 inch and 5 feet 7 inches. That’s one standard deviation. Ninety-five percent are within two standard deviations of the average, between 4 feet 10 inches and 5 feet 10 inches. And 99.7 percent are no more than three standard deviations away from the average, between 4 feet 6 inches and 6 feet 2
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