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Answer

When deviations from the average are reported, such figures are of no use without some measure of spread. If the standard deviation of the weight of one-year-old boys is three pounds, then this particular child's weight is unremarkable; if the standard deviation is one pound, then it may be a matter of concern. In fact, the standard deviation is much closer to three pounds than to one pound, so there is nothing to worry about. (Source: J. M. Tanner (1978), Foetus into Man. London: Open Books.)

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