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Classical Test Theory vs Item Response Theory

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Chris Allred

on 23 April 2011

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Transcript of Classical Test Theory vs Item Response Theory

Zickar, M. J. & Broadfoot, A. A. (2009). The partial revival of a dead horse? Comparing classical test theory and item response theory. In C. Lance and R. J. Vandenberg (Eds.), Statistical and Methodological Myths and Urban Legends (pp. 37-60). New York: Routledge. CTT vs IRT in Media What to Expect from this Presentation:

Assumptions and principles of each theory

Criticisms and limitations of both theories

Scenarios and situations where each theory is preferable
Assumptions and principles of each theory : Classical Test Theory

X = T + E
the scale score is the unit of analysis

Assumes the following:
true scores and error scores are uncorrelated
error scores
reliability- SEoM Assumptions and principles of each theory – Item Response Theory

Focus is on the item...(IRT)

Assumes the following:
Test or measure is unidimensional
Local independence is present IRT – Item Response Function

item difficulty
item discrimination
Criticisms and limitations of both theories – Classical Test Theory

Sample and test dependent
Person and item parameters on differing scales
Parameters often confounded with one another
Reliability Criticisms and limitations of both theories – Item Response Theory

Sample size requirements
Strong assumptions
Practical problems with software

Times to use Classical Test Theory

Small sample sizes
Multidimensional data?
CTT supports other methodologies

Structural Equation Modeling
Confirmatory Factor Analysis
Exploratory Factor Analysis

Times to use Item Response Theory

Attention to a particular range of the construct
Conducting Goodness-of-Fit Studies
Supports many psychometric tools
Differential Item Functioning
Computer Adaptive Testing Take Home Points:

IRT does have many advantages compared to CTT
Just because a statistical device is more powerful doesn’t mean it’s always preferable
Often CTT and IRT provide similar answers
CTT still a legitimate choice in many situations

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