Sunday, February 2, 2014

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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