Returns on an investor's stock portfolio (n = 19 stocks)are compared for the same stock in each of two consecutive quarters.Since the returns are not normally distributed (normality test p-values were .005 and .126 respectively),a nonparametric test was chosen.The test results are shown below. Which is the best conclusion?
A) The means are the same at α = .01.
B) The medians are the same at α = .01.
C) The means differ at α = .01.
D) The medians differ at α = .01.

Question

Returns on an investor's stock portfolio (n = 19 stocks)are compared for the same stock in each of two consecutive quarters.Since the returns are not normally distributed (normality test p-values were .005 and .126 respectively),a nonparametric test was chosen.The test results are shown below.  Which is the best conclusion?
A) The means are the same at α = .01. 
B) The medians are the same at α = .01. 
C) The means differ at α = .01. 
D) The medians differ at α = .01.

Quizplus · Accepted Answer

Since the returns are not normally distributed, a nonparametric test was used. The Wilcoxon signed-rank test is a nonparametric test used to compare two related samples. The test result shows that the p-value is less than .01, indicating that there is a significant difference in returns. Since the test is nonparametric, it compares the medians and not the means. Therefore, the best conclusion is that the medians differ at α = .01, which is choice D.

Returns on an Investor's Stock Portfolio (N = 19 Stocks)are