Statistics > Measuring Spread: Range, IQR, Standard Deviation
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QuickNotes™ 
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.
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