Additivity in Psychological Measurement

Shows how the Rasch model i s a u n i t m a i n t a i n i n g process (Thurstone, 1931) which enables the construct i o n of a d d i t i v i t y (Campbell, 1920) and hence fundamental measurement (Luce and Tukey, 1964). Provides the b a s i c s t a t i s t i c s f o r determining the extent to which a d d i t i v i t y has been approximated w i t h p a r t i c u l a r data. (A note reviews the obstacles to maint a i n i n g u n i t s or c o n s t r u c t i n g a d d i t i v i t y encountered by binomial response models with more than one item parameter.)