Answer: Efficient

## Explanation This question tests the understanding of statistical properties of estimators. **Key Definitions:** - **Efficient Estimator**: An unbiased estimator that has the smallest possible variance among all unbiased estimators of the same parameter. This is exactly what the question describes. - **Unbiased Estimator**: An estimator whose expected value equals the true parameter value. While the question mentions "unbiased estimators," it's describing a property beyond just being unbiased. - **Consistent Estimator**: An estimator that converges in probability to the true parameter value as sample size increases. - **Reliable**: This is not a formal statistical property of estimators in the same sense as the other terms. **Why B is Correct:** The question specifically states that the estimator has "smaller variance than all other unbiased estimators." This is the precise definition of an **efficient estimator** in statistics. An efficient estimator achieves the Cramér-Rao lower bound, which represents the minimum possible variance for an unbiased estimator. **Why Other Options are Incorrect:** - **A (Reliable)**: Not a formal statistical property of estimators - **C (Unbiased)**: While the estimator is unbiased (as mentioned in the comparison), the question is asking about the specific property of having minimum variance among unbiased estimators - **D (Consistent)**: Consistency relates to convergence properties as sample size increases, not specifically to having minimum variance among unbiased estimators This concept is fundamental in statistical inference and is particularly important in the context of maximum likelihood estimation and the Gauss-Markov theorem in regression analysis.

Author: LeetQuiz .