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Z is a standardized measure of the distance
between the rank sum of the negative group and its expected value.
The expected rank sum is 45.5, half the sum of all ranks.
The standard deviation is 14.31.
The negative group rank sum equals 31, so the Z statistic is (31 - 45.5) / 14.31, or -1.013.
From this analysis, the investment analyst can breathe a sigh of relief. His technology stock holdings did not underperform on a daily basis in the years 2000 and 2001, compared to the median daily performance of all other stocks on the S&P 500 over the same period. |
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Wilcoxon Signed-Ranks Test Table |