The Pearson product-moment correlation coefficient was used to measure the bivariate relationship between the tractor stability results, and age, experience and frequency operating a tractor, and gender (Table 6). Results indicate that frequency was unrelated to the tractor stability results. Although age, gender, and experience were unrelated to the reported angle for uncomfortable and would not drive, all three variables were significantly related to the measured angle for uncomfortable and unwillingness to drive. Results indicate that older participants set higher limits on the actual angle they felt uncomfortable and would not drive (r = .23; P = .040 and r = .22; P = .043, respectively). Consistent with the results for age, participants with more experience operating a tractor had higher limits for uncomfortable and would not drive (r = .29; P = .009 and r = .32; P = .003, respectively). Also, male participants set higher limits than females on the actual angle they felt uncomfortable and would not drive (r = −.30; P = .007 and r = −.26; P = .022, respectively).
The results for measured angles are illustrated in Figure 3; it presents the mean measured angles for uncomfortable and would not drive for participants in different age categories, experience categories, and by gender.