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On the Reliability of Testlet-Based Tests IRT

Sireci, Stephen G.; Thissen, David; Wainer, Howard
Publication Year:
Report Number:
RR-91-22, PSRTR-91-10
ETS Research Report
Document Type:
Page Count:
Subject/Key Words:
Item Response Theory (IRT), Statistical Analysis, Test Reliability, Test Theory, Testlets


If a test is constructed of testlets, one must take into account the within-testlet structure in the calculation of test statistics. Failing to do so may yield serious biases in the estimation of such statistics as reliability. In this paper we demonstrate how to calculate the reliability of a testlet-based test. We show that traditional reliabilities calculated on two reading comprehension tests constructed of four testlets are substantial overestimates. (15pp.)

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