Question 125783
Using N as the denominator gives a smaller variation 
of the normal spread of the data; we can have confidence
in this smaller spread because the data is the entire 
population being considered.
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Using n-1 as the denominator gives a larger variation
of the normal spread of the data; we are less confident
of the actual spread of the population data because
we have only a sample.
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Cheers,
Stan H.