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The scale is then obtained as a left-adjusted column marginal average of this standard score matrix (Thurstone, 1927b). The underlying rationale for the method and basis for the measurement of the "psychological scale separation between any two stimuli" derives from Thurstone's Law of comparative judgment (Thurstone, 1928).
Likert scale – Respondents are asked to indicate the amount of agreement or disagreement (from strongly agree to strongly disagree) on a five- to nine-point response scale (not to be confused with a Likert scale). The same format is used for multiple questions. It is the combination of these questions that forms the Likert scale.
Many large-scale clinical tests are normed. For example, scores on the MMPI are rescaled such that 50 is the middlemost score on the MMPI Depression scale and 60 is a score that places the individual one standard deviation above the mean for depressive symptoms; 40 represents a symptom level that is one standard deviation below the mean. [30]
The essential idea behind Thurstone's process and model is that it can be used to scale a collection of stimuli based on simple comparisons between stimuli two at a time: that is, based on a series of pairwise comparisons. For example, suppose that someone wishes to measure the perceived weights of a series of five objects of varying masses.
In fact, there may also appear phenomena which even question the ordinal scale level in Likert scales. [21] For example, in a set of items A, B, C rated with a Likert scale circular relations like A > B, B > C and C > A can appear. This violates the axiom of transitivity for the ordinal scale.
The BTL model is identical to Thurstone's model if the simple logistic function is used. Thurstone used the normal distribution in applications of the model. The simple logistic function varies by less than 0.01 from the cumulative normal ogive across the range, given an arbitrary scale factor.
A rating scale is a set of categories designed to obtain information about a quantitative or a qualitative attribute. In the social sciences , particularly psychology , common examples are the Likert response scale and 0-10 rating scales, where a person selects the number that reflecting the perceived quality of a product .
Another shortcoming lies in the definition of reliability that exists in classical test theory, which states that reliability is "the correlation between test scores on parallel forms of a test". [5] The problem with this is that there are differing opinions of what parallel tests are.