Question

The first four deviations from the mean in a sample of n = 5 reaction times were 0.4, 0.9, 1.0, and 1.3. what is the fifth deviation from the mean?

Answer 1

The sum of standard deviations from the mean of all the observations must be equal to zero. The sum of deviations for the first four points is (0.4+0.9+1.0+1.3)=3.6; so the fifth deviation from the mean should be -3.6 so that the total sum of standard deviation will be zero.