Comparisons of category scales employed for opinion rating

Comparisons have been made between three category scales that have been used for the laboratory assessment of impaired television pictures. Two of the scales, comprising 5 and 6 grades, respectively, are concerned with assessment of the quality of the picture; the third is a 6-grade scale concerned with assessment of the amount of impairment in the picture. In one group of tests, observers assessed television pictures impaired by an undistorted echo of delay 2 ¿s, and, in another, photographic prints affected by varied amounts of blurring. Various combinations of the scales were used in each group. The 5-grade and 6-grade quality scales gave closely similar results in terms of mean opinion scores, but these results differed from those obtained with the 6-grade impairment scale, which were less critical. Observers preferred the 5-grade quality scale to both of the 6-grade scales.