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among them are average, mean and central tendency. By any

name, the calculation is the same: the values are summed up and

the total is divided by the number of values (see the equation on

the left below). For many measures, especially in education and

economics, average is nearly useless and is often deceptive instead

of descriptive. A preferred treatment is to also provide what are

called higher order moments about the mean. The second moment

is called the variance (see the equation on the right below), while

the third moment measures skewness, the fourth tailedness, and

the fifth and sixth moments various further parameters of the

extremes of the values.