The advantages that computer adaptive testing offers over linear tests have been well documented. The Computer Adaptive Test (CAT) design is more efficient than the Linear test design as fewer items are needed to estimate an examinee's proficiency to a desired level of precision. In the ideal situation, a CAT will result in examinees answering different number of items according to the stopping rule employed. Unfortunately, the realities of testing conditions have necessitated the imposition of time and minimum test length limits on CATs. Such constraints might place a burden on the CAT test taker resulting in aberrant response behaviors by some examinees. Occurrence of such response patterns results in inaccurate estimation of examinee proficiency levels. This study examined the effects of test lengths, time limits and the interaction of these factors with the examinee proficiency levels on the occurrence of aberrant response patterns. The focus of the study was on the aberrant behaviors caused by rushed guessing due to restrictive time limits. Four different testing scenarios were examined; fixed length performance tests with and without content constraints, fixed length mastery tests and variable length mastery tests without content constraints. For each of these testing scenarios, the effect of two test lengths, five different timing conditions and the interaction between these factors with three ability levels on ability estimation were examined. For fixed and variable length mastery tests, decision accuracy was also looked at in addition to the estimation accuracy. Several indices were used to evaluate the estimation and decision accuracy for different testing conditions. The results showed that changing time limits had a significant impact on the occurrence of aberrant response patterns conditional on ability. Increasing test length had negligible if not negative effect on ability estimation when rushed guessing occured. In case of performance testing high ability examinees while in classification testing middle ability examinees suffered the most. The decision accuracy was considerably affected in case of variable length classification tests. (PsycINFO Database Record (c) 2003 APA, all rights reserved).