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)

Theta

Assumes the following:

Test or measure is unidimensional

Local independence is present IRT – Item Response Function

Parameters:

item difficulty

item discrimination

pseudo-guessing

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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# Classical Test Theory vs Item Response Theory

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