Item selection rules in computerized adaptive testing: Accuracy and security

The item selection rule (ISR) most commonly used in computerized adaptive testing (CAT) is to select the item with maximum Fisher information for the current trait estimation (PFI). Several alternative ISRs have been proposed. Among them, Fisher information considered in an interval (FI*I), Fisher information weighted with the likelihood function (FI*L), Kullback-Leibler information considered in an interval (KL*I) and Kullback-Leibler weighted with the likelihood function (KL*L) have shown a greater precision of trait estimation at the early stages of CAT. A new ISR is proposed, Fisher information by interval with geometric mean (FI*IG), which tries to rectify some detected problems in FI*I. We evaluate accuracy and item bank security for these six ISRs. FI*IG is the only ISR which simultaneously outperforms PFI in both variables. For the other ISRs, there seems to be a trade-off between accuracy and security, PFI being the one with worse accuracy and greater security, and the ISRs using the likelihood function the reverse. © 2009 Hogrefe & Huber Publishers.