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MODULE 1: WHY STEVENS? THE CONTEXT OF 1946 Before 1946, measurement outside physics lacked a clear warrant. Campbell addressed additivityfor manifest quantities; psychophysics mapped sensations; operationalism equated meaning withprocedure. None guaranteed that numerals preserved empirical structure or justified arithmetic,particularly for latent traits. Stevens resolved this by linking scale types—nominal, ordinal,interval, ratio—to permissible arithmetic and statistics. He did not provide a method forconstructing invariant rulers for latent attributes. That gap was later filled by the axiomatic workin Foundations of Measurement and by Rasch

A NEW START IN MEASUREMENT  FOR HEALTH TECHNOLOGY ASSESSMENT For fifty years, HTA has confused numbers with measures. Scientific practice requires adherenceto representational measurement theory, from Stevens’ linkage of arithmetic to scale type to therepresentation and uniqueness theorems of Krantz, Luce, Suppes, and Tversky. Rasch providedthe operational bridge for latent traits, transforming ordered responses into an invariant logitruler. HTA instead fixated on QALYs and multiattribute valuations, guaranteeing persistentfailure. The remedy is non-negotiable: only linear ratio scales for manifest claims and Raschlogit ratio