The Effect of Person Misfit on Item Parameter Estimation and Classification Accuracy: A Simulation Study

Often, important decisions regarding accountability and placement of students in performance categories are made on the basis of test scores generated from tests, therefore, it is important to evaluate the validity of the inferences derived from test results. One of the threats to the validity of such inferences is aberrant responding. Several person fit indices were developed to detect aberrant responding on educational and psychological tests. The majority of the person fit literature has been focused on creating and evaluating new indices. The aim of this study was to assess the effect of aberrant responding on the accuracy of estimated item parameters and refining estimations by using person fit statistics by means of simulation. Our results showed that the presence of aberrant response patterns created bias in the both b and a parameters at the item level and affected the classification of students, particularly high-performing students, into performance categories regardless of whether aberrant response patterns were present in the data or were removed. The results differed by test length and the percentage of students with aberrant response patterns. Practical and theoretical implications are discussed.