Calculating the bias of a statistic?

I am asked to calculate the bias of a statistic. I understand that the bias is the difference between the estimator and the actual value of the parameter.


in my case i am supposed to calculate the bias of


S=squareroot(sum(xi-xmean)^2/(n-1)) and


S'=S=squareroot(sum(xi-xmean)^2/(n)).





it is to be proven that S is less bias than S'.|||use the Pearson's chi square test