ABSTRACT
This chapter provides the principles of invariant measurement within the context of rating scales and rater judgments. It argues that Guilford's concept of a continuum can be operationally defined in the form of a Wright map that can be used to represent a latent variable or construct. The chapter examines the use of the concept of invariance to highlight commonalities across different issues encountered in measurement in the social sciences. The basic structure of rater-mediated assessments should include an explicit consideration of two theoretical frameworks: a conceptual model of the judgmental processes of the raters and a measurement model for ratings within the assessment system. In many ways, the rater-invariant Wright map can be viewed as the main outcome of building a rater-mediated assessment system that meets the requirements of invariant measurement. The graphic rating scale is similar to the numerical rating scale with the rater actually seeing a horizontal line representing the continuum, and then locating persons on this continuum.
