Runs test table, cut point = median
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  • The test value is used as a cut point to dichotomize the sample. In this table, the cut point is the sample median.
  • Of 32 testers, 14 scored below the median. Think of them as the "negative" cases.
  • The remaining 18 testers scored at or above the median. Think of them as the "positive" cases.
  • The next statistic is a count of the observed runs in the test variable. A run is defined as a sequence of cases on the same side of the cut point.
  • For example, looking at the data, you observe that the first four cases are below the median. This sequence of four "negatives" is the first run.
  • The second run begins at case 5, whose Web site rating is equal to the median.
  • The third run begins at case 6, which is again below the median. Counting continues in the same way across all 32 cases in the file.
  • If the order of the ratings is purely random with respect to the median value, you would expect about 17 runs across these 32 cases. Because you observed only 10 runs, the Z statistic is negative.
  • The 2-tailed significance value is the probability of obtaining a Z statistic as or more extreme (in absolute value) than the obtained value, if the order of ratings above and below the median is purely random.