Actually, I dont' think that's correct
Message #1 Posted by Gene on 27 Mar 2003, 10:04 a.m.
The formula for standard deviation of a sample has n-1 on the denominator, so it should work for 2 data points.
Suppose the data are 10 and 5
Standard deviation is
SQRT ((( 10 - 7.5 ) ^2 + (5 - 7.5) ^2) divided by (2 - 1))
Which works out to be 2.5
Granted, that's not exactly helpful with only 2 data points, but it does work.
Population standard deviation only has n on the denominator, so you can compute it when you only have 1 data point...the value of the standard deviation in that instance would be 0.
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