Item exposure constraints for testlets in the verbal reasoning section of the MCAT

The current study examined item exposure control procedures for testlet scored reading passages in the Verbal Reasoning section of the Medical College Admission Test with four computerized adaptive testing (CAT) systems using the partial credit model. The first system used a traditional CAT using maximum information item selection. The second used random item selection to provide a baseline for optimal exposure rates. The third used a variation of Lunz and Stahl's randomization procedure. The fourth used Luecht and Nungester's computerized adaptive sequential testing (CAST) system. A series of simulated fixed-length CATS was run to determine the optimal item selection procedure: Results indicated that both the randomization procedure and CAST performed well in terms of exposure control and measurement precision, with the CAST system providing the best overall solution when all variables were taken into consideration.