In 1959, Ragnar Frisch prompted Georg Rasch to formalise a separability theorem that continues today to serve as the basis of a wide range of theoretical and applied developments in psychological and social measurement. Previously unnoted are the influences on Rasch exerted by Frisch’s...

In 1979, the Danish mathematician Georg Rasch recounted a 1959 visit with his former teacher, and later economics Nobel Prize winner, Ragnar Frisch. At this time, Frisch prompted Rasch to formalize his work in a separability theorem. Previously unnoted is that Frisch's close colleague, Irving...