Standard Deviation

Standard deviation can be a little tricky when you are first introduced to it, but it is simply a measure of how dispersed, or far apart from each other, the data points in a set are.  

Low or small standard deviation: Sets where the numbers are clustered near the mean of the set.  

High or large standard deviation: Sets where lots of the numbers are far from the average.

Some examples help to make this clear.

Below are charts detailing the measured weights (in kg) of groups of wombats divided by sex.

The mean for the females is around 24.  Notice how all the values are very close to the average – this represents a low standard deviation.  For the males, the mean is about 25; However, only a couple of our values are close to the mean.  This data set has a much higher standard deviation.

The SAT will not make you calculate the actual standard deviation.  This is a complex job best left for computers.  They will make the answer painfully obvious as long as you have an understanding of what standard deviation is.  

You might also be presented data in graphical form and asked to evaluate standard deviation.