Variance can be
calculated in two ways:
Variance assumes that the returns series is a sample of the population.
This is the calculation most commonly used.
If we denote by 
the mean of
the returns, the variance is:
Var(r1, ..., rn) = 
where r1,
..., rn is a return series, i.e., a sequence of returns for n time
periods.
Population
Variance assumes that the return series is the population.
PVar(r1,
..., rn) = 
Related Statistics:
Annualized Return
Cumulative Return
Mean
Standard Deviation
