APPROXIMATE EXPRESSIONS FOR PARAMETER ESTIMATES IN THE RASCH MODEL

The Wright‐Panchapakesan (1969) maximum‐likelihood equations for estimating the ability and difficulty parameters in the Rasch model have hitherto required an iterative procedure for their solution. In this paper the equations are solved approximately and simple closed forms are established which give values close enough for most practical purposes to those obtained by iteration. The results are illustrated with reference to a 50‐item physics test. 1979 The British Psychological Society