Reading 10: Sampling and Estimation - LOS e ～ Q11-12

答案和详解如下：

11.Joseph Lu calculated the average return on equity for a sample of 64 companies. The sample average is 0.14 and the sample standard deviation is 0.16. The standard error of the mean is closest to:

A)   0.1600.

B)   0.0200.

C)   0.0025.

D)   0.0500.

The correct answer was B)

The standard error of the mean = σ/√n = 0.16/√64 = 0.02.

12.The mean return of Bartlett Co. is 3 percent and the standard deviation is 6 percent based on 20 monthly returns. What is the standard error of the sample and the confidence interval of a two tailed z-test with a 5 percent level of significance?

       Standard error    Confidence Interval

A)                     2.00    0.37 to 5.629

B)                     2.00    -0.66 to 4.589

C)                     1.34   0.37 to 5.629

D)                     1.34    -0.66 to 4.589

The correct answer was C)

The standard error of the sample is the standard deviation divided by the square root of n, the sample size. 6/20^1/2 = 1.34%.

The confidence interval = point estimate +/- (reliability factor × standard error)

confidence interval = 3 +/- (1.96 × 1.34) = 0.37 to 5.629