4. (+3) It can be shown that the sample covariance = an unbiased and consistent estimator of population covariance o. Use these facts to answer the following. (Hint: note that = , and derive the mean and variance of in terms of the mean and variance of S xy.) a. What is the bias of the method of moments covariance estimator = b. Is sigma xy consistent? Justify your answer. 4. (+3) It can be shown that the sample covariance = an unbiased and consistent estimator of population covariance o. Use these facts to answer the following. (Hint: note that = , and derive the mean and variance of in terms of the mean and variance of S xy.) a. What is the bias of the method of moments covariance estimator = b. Is sigma xy consistent? Justify your