Median
From OPOSSEM
if <math>n</math> is even, <math>M = \frac{\text{sum of middle two values in a series}}{2}</math>; if <math>n</math> is odd, <math>M = \frac{n+1}{2}\text{th value in series}</math>
if <math>n</math> is even, <math>M = \frac{\text{sum of middle two values in a series}}{2}</math>; if <math>n</math> is odd, <math>M = \frac{n+1}{2}\text{th value in series}</math>