An operator of a certain machine must turn it off quickly if a danger signal occurs. To test the relative effectiveness of two types of signals, a small group of operators is randomly divided into two groups. Those in Group 1 operate machines with a newly designed signal, while those in Group 2 use machines with the standard signal. The signal is flashed unexpectedly, and the reaction time of each operator (time taken to turn off the machine after the signal occurs) is measured in seconds. The actual results (not ranks) are shown here.

(a) Use the rank-sum test to determine whether there is a significant difference between the two groups.

(b) Compute the appropriate measure of strength of relationship.

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Group 1 Group 2 5 3 17 4 13 10 16 11 3. 3. 2.