With the use of statistical software, many individuals are being exposed to more than just measures of location and dispersion. In addition to the average and standard deviation, they often find some funny numbers labeled as skewness and kurtosis. Since these numbers appear automatically, it is natural to wonder how they might be used in practice. In part one of this two-part column, I'll illustrate what the skewness and kurtosis parameters do. In part two I will look at the use of skewness and kurtosis statistics provided by software packages.

Since the previous sentence makes a distinction between a statistic and a parameter, we should begin there. Statistics are merely functions of the data. We find the value for a statistic by performing a set of arithmetic operations using a set of data. For example, we compute the average for a set of numbers by adding up all the numbers and dividing by the number of values in the sum. Thus, any time we have a collection of numbers we can compute any one of a number of statistics. Data plus arithmetic equals a statistic.

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