Detection of Aberrant Response Patterns and their Effect on Dimensionality

Two indices were developed for measuring the degree of conformity or consistency of an individual examinee’s response pattern on a set of items. The first, called the norm conformity index (NCI), measures the proximity of the pattern to a baseline pattern in which all 0’s precede all l’s when the items are arranged in some prescribed order. The second, called the individual consistency index (ICI), measures the extent to which an individual’s response pattern remains invariant when he or she responds to several waves of parallel items. We show how these two indices, used in conjunction with test scores, can spot aberrant response patterns of students requiring detailed error diagnosis and remedial treatment.