Newton-Raphson step size = 0

Facets uses Joint Maximum Likelihood Estimation (JMLE) or a Facets implementation of PMLE to estimate the Rasch measures from ordinal data. This requires an iterative process. Initial estimates are imputed for all the element measures. The expected observations are computed based on these estimates and totaled for each element. Then for each element, the observed and expected total scores are compared, and the element measure re-estimated to a value intended to make the expected total score the same as the observed total score. This process is repeated until the differences between the observed and the expected total scores are too small to matter. This is called convergence.

 

Initial estimates are obtained using the PROX (normal approximation) algorithm.

 

More exact estimates are obtained using iterative curve fitting (when Newton=0) or the Newton-Raphson method. Newton= can be set using the Estimation menu.