We are interested in determining the population mean using a sample of size n. Consider two alternative estimators of the population mean:
(i) the first one uses the first observation of the sample;
(ii) the second one uses the simple average of the first and last observation of the sample.
Only the second estimator is unbiased. The second estimator is more efficient than the first one.
Only the first estimator is unbiased. It is more efficient than the second one.
Both estimators are unbiased. The second one is more efficient than the first one.
Both estimators are unbiased. The first one is more efficient than the second one.