The “New Psychometrics” – Item ResponseTheory

Classical test theory is concerned with the reliability of a test and assumes that the items

within the test are sampled at random from a domain of relevant items. Reliability is seen

as a characteristic of the test and of the variance of the trait it measures. Items are treated

as random replicates of each other and their characteristics, if examined at all, are expressed

as correlations with total test score or as factor loadings on the putative latent variable(s) of

interest. Characteristics of their properties are not analyzed in detail. This led Mellenbergh

(1996) to the distinction between theories of tests (Lord and Novick, 1968) and a theories

of items (Lord, 1952; Rasch, 1960). The so-called “New Psychometrics” (Embretson and

Hershberger, 1999; Embretson and Reise, 2000; Van der Linden and Hambleton, 1997) is a

theory of how people respond to items and is known as Item Response Theory or IRT. Over

the past twenty years there has been explosive growth in programs that can do IRT, and

within R there are at least four very powerful packages: eRm (Mair and Hatzinger, 2007),

ltm Rizopoulos(2006), lme4 (Doran et al., 2007) and MiscPsycho, (Doran, 2010). Additional

packages include mokken (van der Ark, 2010) to do non-metric IRT and plink (Weeks, 2010)

to link multiple groups together. More IRT packages are being added all of the time.

Topics covered:

Chapter 8 - The “New Psychometrics” – Item ResponseTheory

Chapter 9 - Validity

Chapter 10 - Reliability + Validity = Structural Equation Models

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