This article critically reviews how diagnostic models have been conceptualized and how they compare to other approaches used in educational measurement. In particular, certain assumptions that have been taken for granted and used as defining characteristics of diagnostic models are reviewed and it is questioned whether these assumptions are the…

This commentary examines the role of the unit from the perspective of the definition of measurement in physics as the ratio of two magnitudes, one of which is defined as the unit; it is an important and timely contribution to measurement in the social sciences. There are many different points that could be commented upon, but the author will…

Compared to traditional test theory, where person measures are typically referenced to the distribution of a population, item response theory allows for a much more meaningful interpretation of measures as they can be directly compared to item locations. However, Stephen Humphry shows that the crucial role of the unit of measurement has been…

Humphry (this issue) deserves credit for drawing attention to the long-neglected fact that differences in item discrimination parameters are often due to empirical factors and not the product of random error components. In doing so, Humphry offers a psychometrically elegant, coherent, and practically important new model that is more flexible while…

Humphry (this issue) has written a thought-provoking piece on the interpretation of item discrimination parameters as scale units in item response theory. One of the key features of his work is the description of an item response theory (IRT) model that he calls the logistic measurement function that combines aspects of two traditions in IRT that…

Behavioral scientists have struggled with units of measurement for as long as they have struggled with measurement itself. Psychology's sole attempt at an explicit unit of measurement--the Lexile Framework for Reading (Stenner, Burdick, Sanford, & Burdick, 2006)--has been and continues to be ignored by the psychometric "cognoscenti."…

The purpose of this article is to examine the role of the unit in physics in order to clarify the role of the unit in psychometrics. Based on this examination, metrological conventions are used to formulate the relationship between discrimination and the unit of a scale in item response theory. Seminal literature in two lines of item response…

This article presents Stephen Humphry's response to the commentaries for his article "The Role of the Unit in Physics and Psychometrics." The commentaries covered a range of important considerations and implications. Given that the author fully agrees with the majority of the content, attention will be confined mainly to points that call…

In their paper "Unique Characteristics of Diagnostic Classification Models: A Comprehensive Review of the Current State-of-the-Art," Andre Rupp and Jonathan Templin (2008) provide a comparative analysis of selected psychometric models useful for the analysis of multidimensional data for purposes of diagnostic score reporting. Recent assessment…

Paul Newton (2010), with his characteristic concern about theory, has set out two different ways of thinking about the basis upon which equivalences of one sort or another are established between test score scales. His reason for doing this is a desire to establish "the defensibility of linkages lower on the continuum than concordance."…

This article presents the author's rejoinder to thinking about linking from issue 8(1). Particularly within the more embracing linking frameworks, e.g., Holland & Dorans (2006) and Holland (2007), there appears to be a major disjunction between (1) classification discourse: the supposed basis for classification, that is, the underlying theory…

"Linking" is a term given to a general class of procedures by which one represents scores X on one test or measure in terms of scores Y on another test or measure. A recent taxonomy by Holland and Dorans (2006; Holland, 2007) organizes the various types of links into three broad categories: prediction, scale aligning, and equating. In…

Newton's article (2010) makes three main contributions to the literature. First, it is transatlantic, bringing together literatures that have been dealing with similar problems, using sometimes different methods and certainly with distinctive educational, cultural perspectives. He points out that neither of these literatures has all of the…

The article "Thinking About Linking" by Newton (2010) presents a novel philosophical perspective on the way that educational assessments should be linked. Newton starts by describing the linking framework as it was characterized in various publications and identifies a cross-cultural dimension in the definitions and uses of test…