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Measuring Spread: Range, IQR, Standard Deviation

• Range is the simplest way to calculate the spread of a distribution. It is also extremely influenced by outliers.

• Before calculating the standard deviation, calculate the variance. Make sure whether you need to find the population variance and standard deviation or a sample variance or standard deviation.

• Before calculating the interquartile range, make sure that the data are ordered from lowest to highest.

• The standard deviation is the best measure of spreads since it uses all of the observations; however, if the data are skewed, the interquartile range is the preferred measure of the center.