An experimental investigation was conducted for the combined purposes of determining the relative merits of various category scales for the prediction of human discomfort response to vibration and for determining mathematical relationships whereby subjective data are transformed from one _cale to other scales. There were 16 category scales analyzed in this study representing various parametric combinations of polarity, that is, unipolar and bipolar, scale type (continuous or discrete), and number of scalar points (three, five, seven, or nine). Sixteen subject groups (12 subjects per group) were used, and each subject group evaluated their comfort or discomfort to vertical sinusoida] vibrations by using one of the rating scales. The experimental apparatus utilized was the Langley passenger ride quality apparatus which can expose six subjects simultaneously to predetermined vibrations. For this study, the vibration stimuli were composed of repeats of eight selected sinusoidal frequencies (1, 2, 4, 5, 8, 10, 15, and 20 Hz) applied at each of nine peak floor acceleration levels (0.05, 0.075, 0.10, 0.125, 0.15, 0.175, 0.20, 0.225, and 0.25 g).

Results indicated that unipolar continuous-type scales containing either seven or nine scalar points provide the greatest reliability and discriminability. Furthermore, transformations of subjective data between category scales were found to be feasible with unipolar scales of a larger number of scalar points providing the greatest accuracy of transformation. The results contain coefficients for transformation of subjective data between the category scales investigated. A result of particular interest was that the comfort (or positive) half of a bipolar scale was seldom used by subjects to describe their subjective reaction to vibration.