Conditional Versus Unconditional Procedures for Sample-Free Item Analysis

Abstract

Two procedures for Rasch, sample-free, item calibration are reviewed and compared for accuracy. Andersen's (1972) theoretically ideal "conditional" procedure is impractical for calibrating more than 10 or 15 items. A simplified alternative procedure for conditional estimation practical for 20 or 30 items which produces equivalent estimates is developed. When more than 30 items are analyzed recourse to Wright's (1969) widely used "unconditional" procedure is inevitable but that procedure is biased. A correction factor which makes the bias negligible is identified and demonstrated.