Scaling of Subjective Credibility: A Prothetic Continuum

Abstract

To determine the scalability of a subjective credibility dimension pertaining to psychometric test-item statements and also whether such a judgmental dimension could be classified as being metathetic or prothetic, student judges made magnitude estimations of the subjective credibility of items on the Opinions about Mental Illness Scale with respect to a standard item statement (modulus value = 50). Judges were randomly divided into two groups with respect to the magnitude-estimation task, one group presented with a reversed order of stimuli. Each judge also made category scale judgments of the stimuli on a five-point credibility category scale. The judgmental credibility continuum possessed high intrascale and interscale reliability. With such high reliability, item statements can be legitimately scaled with respect to a subjective credibility judgmental dimension. The judgmental continuum was considered to be prothetic based on two criteria, a concave downward relationship between the category and magnitude-estimation scales and a positive relationship between judgmental variability and subjective magnitude.