Abstract
The purpose of this research was to explore psycho metric issues pertinent to the application of an IRT based person-fit (response aberrancy) detection statistic in the personality measurement domain. Monte carlo data analyses were conducted to address issues regarding the l z person-fit statistic. The major issues explored were characteristics of the null distribution of l z and its power to identify nonfitting response patterns under different scoring strategies. There were two main results. First, the l z index null distribution was not well standardized when item parameters of personality scales were used; the l z null distribution variance was significantly less than the hypothesized value of 1.0 under several conditions. Second, the power of l z to detect response misfit was affected by the scoring method. Detection power was optimal when a biweight estimator of θ was used. Recommendations are made regarding proper implementation of person-fit statistics in personality measurement.
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