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...

Reliability coefficients indicate the proportion of total variance due to differences not attributable to error among measures separated along a quantitative continuum by a testing, survey, or assessment instrument. Person score or measure reliability is influenced by both the internal...