ASM, exercise 19.11 (Review of Mathematical Statistics) I have
the 11th edition. The question reads (with simplification): A
population contains the values 1, 2, 4, 9. A sample of 3 is
withdrawn without replacement from this variable. Calculate the
mean square error of the median of this sample as an estimator
of the population mean. The solution is: half the time the
sample median is 2 and the other half the time it is 4. The mean
of the population is 4. So the MSE is 1/2*(2-4)^2=2. I don't
understand the last step. Is there a Bernoulli shortcut
involved.