D. Implementation of Item Parameter Estimation via MMLE/EM
In order to provide a concrete illustration of the Bock and Atkin's (1981) marginal maximum likelihood estimation (MMLE) / expectation-maximization (EM) approach, a BASIC computer program was developed. This computer program, based on programs due to Zwarts (1986), has been written specifically to handle the LSAT-6 data set reported by Bock and Lieberman (1970). This data set is composed of the responses of 1000 examinees to five dichotomous items. The current computer program was designed for didactic purposes only, and the reader is referred to BILOG (Mislevy & Bock, 1986) for a production program. It is assumed that the computer is equipped with a math-coprocessor chip since without it, the numerical calculations will be very time-consuming.