Two proposed computer mouse designs were compared by recording wrist extension in degrees for 24 people who each used both mouse types (“Comparative Study of Two Computer Mouse Designs,” Cornell Human Factors Laboratory Technical Report RP7992). The difference in wrist extension was computed by subtracting extension for mouse type B from the wrist extension for mouse type A for each student. The mean difference was reported to be 8.82 degrees. Assume that it is reasonable to regard this sample of 24 people as representative of the population of computer users.
a. Suppose that the standard deviation of the differences was 10 degrees. Is there convincing evidence that the mean wrist extension for mouse type A is greater than for mouse type B? Use a .05 significance level.
b. Suppose that the standard deviation of the differences was 26 degrees. Is there convincing evidence that the mean wrist extension for mouse type A is greater than for mouse type B? Use a .05 significance level.
c. Briefly explain why a different conclusion was reached in the hypothesis tests of Parts (a) and (b).