Pooled sample variance
Where analyses are performed on two or more samples with different concentrations, a polled variance can be used
s2pooled = [(n1 - 1) s12 + (n2 - 1 ) s22 ] / [ (n1 - 1) + (n2 - 1 ) ]
Then MDL = t n1+n2-2, 0.01 spooled
Valid if variances are statically the same