Final answer:
Using '+' and '-' signs as a PT, the ratio scale is the most objective because it allows for meaningful comparison and calculation of ratios due to its true zero point.
Step-by-step explanation:
If we decide to use '+' and '-' as indicators for a Performance Task (PT), the most objective scale would be the ratio scale. The ratio scale is valuable because it not only allows for meaningful differences between data points, as seen with interval scales, but also has a true zero point enabling the calculation of meaningful ratios. For instance, in the case of exam scores of 80, 68, 20, and 92, we can accurately say that a score of 80 is four times that of 20, demonstrating the utility of ratio scales in providing the most information.
An example of utilizing this scale in psychological testing could be the recording of differencing weights in Just-Noticeable-Difference (JND) Testing. Participants might be presented with a certain weight (base weight) and then be asked whether subsequent weights (step weights) are perceived differently; where a '+' indicates a perceived difference and a '-' indicates no perceived difference. This method introduces an objective way of quantifying the ratio differences in subjective perception.
The use of ratio scales, as opposed to nominal or ordinal scales, allows for the most precise and objective analysis in statistical measurements, as meaningful comparisons, differences, and ratios can be computed without ambiguity.