Tractor rollover protection. Refer to the Human Factors (February 2020) study of the incorrect usage of tractor foldable rollover protection structures (FROPS), Exercise 11.23 (p. 641). Recall that a sample of 20 farmers were recruited to drive tractors with FROPS installed. Two variables were measured: y = the vertical distance (in millimeters) from the FROPS pivot pin to the top of the FROPS when in an upright position and x = the farmer’s working experience (in years). The data (simulated from information provided by the study) are reproduced in the next table

a. Rank the values of pivot pin-top distance (y).

b. Rank the values of farmer’s working experience (x).

c. Based on the ranks, compute Spearman’s rank correlation coefficient between pivot pin-top distance and working experience.

d. Is there evidence of positive rank correlation between the pivot pin-top distance and a farmer’s working experience? Test using a = .10.