Like the mean , is not resistant. A few outliers can make very large. The use of squared deviations makes even more sensitive than to a few extreme observations.
Ex: The standard deviation of the travel times for the 15 New York State workers is 21.88 minutes. If we omit the maximum value of 85 minutes, the standard deviation drops to 18.34 minutes.
measures spread about the mean and should be used only when the mean is chosen as the measure of center.
only when there is no variability. This happens only when all observations have the same value.
. As the observations become more 
, which is in squared calories.
