Suppose a measurement is made on some physical characteristic whose value is known, and let X denote the resulting measurement error. For an unbiased measuring instrument or technique, the mean value of X is 0. Assume that any particular measurement error is normally distributed with variance s². Let X1, . . . Xn be a random sample of measurement errors.

a. Obtain the method of moments estimator of s².

b. Obtain the maximum likelihood estimator of s².