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Item Response Theory Fundamentals

This book provides a practical and accessible introduction to Item Response Theory (IRT), a modern measurement framework that overcomes the limitations of classical test theory to enable more precise, fair, and efficient psychological and educational assessment.

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What it’s about

Fundamentals of Item Response Theory offers a comprehensive yet accessible guide to the powerful psychometric framework that has revolutionized educational and psychological testing. It systematically addresses the shortcomings of classical test theory, such as sample-dependent item statistics and test-dependent ability scores, and presents IRT as a superior alternative. Readers will learn the core concepts, models (one-, two-, and three-parameter logistic), and assumptions of IRT, alongside practical guidance on parameter estimation, model-fit assessment, and the interpretation of ability scales. The book then demonstrates the utility of IRT in solving complex measurement problems, including test construction, identifying biased items, equating test scores, and designing computerized adaptive tests, making it an essential resource for measurement practitioners, researchers, and students seeking to understand and apply modern assessment methods.

The through-line

Who it’s for
A measurement practitioner, test developer, or researcher who uses classical test theory but is frustrated by its limitations. They want to build higher quality, more efficient, and fairer tests, and need to understand and apply modern psychometric methods to solve complex testing problems.
The problem
Classical test methods produce group-dependent item statistics and test-dependent ability scores, making it difficult to build robust item banks, equate different test forms, and construct tests with specified precision. They feel uncertain and perhaps intimidated by the complexity of modern measurement theories, worrying their methods are outdated and that their tests may not be technically defensible against challenges.
The plan
  1. Learn the fundamental concepts and models of IRT.
  2. Master the procedures for estimating parameters and assessing how well the model fits your data.
  3. Apply IRT to solve key measurement challenges: building better tests, detecting item bias, equating scores, and implementing adaptive testing.
The payoff
They can design and build technically superior tests with specified levels of precision across the ability spectrum. · They are able to create robust item banks with invariant item parameters, enabling fair comparisons and efficient test development. · They can confidently equate different test forms, detect biased items, and implement advanced applications like computerized adaptive testing.

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