Teacher’s Corner: Origin of the Scaling Constant d = 1.7 in Item Response Theory
Gregory Camilli · Journal of Educational and Behavioral Statistics · 1994
The scaling constant d = 1.702 used in item response theory minimizes the maximum difference between the normal and logistic distribution functions. The theoretical and numerical derivation of d given by Haley (1952) is briefly recapitulated to provide access to curious researchers, instructors, and students.