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Europa Medicophysica 2003 December;39(4):201-4

Copyright © 2003 EDIZIONI MINERVA MEDICA

language: English

Case-mix classification systems. The specific case for rehabilitation

Tesio L. ^{1, 2}

¹ Unit of Neuromotor Rehabilitation Istituto Auxologico Italiano, IRCCS, Milan, Italy 2 Department of Rehabilitation Medicine and Socio-medical Services, CRISP Centro di Ricerca Interuniversitario sui Servizi alla Persona di Pubblica Utilità, Milan, Italy

The ­case-mix clas­sifi­ca­tion con­sists in iden­ti­fying a ­series of clin­ical con­di­tions, so ­that ­they can be uni­vo­cally clus­tered in ­groups ­which are mutu­ally exclu­sive. Homo­ge­neous con­di­tions are ­assigned to the ­same “group” or “­class”. The cri­teria for homo­ge­neity can be ­much dif­ferent, ­depending on the ­goal of the clas­sifi­ca­tion ­itself. ­Many ­grouping ­systems are acknowl­edged inter­na­tion­ally. ­They may ­follow the cri­terion of homo­ge­neity ­with ­respect to aetio­logy (ICD ­system), ­resource con­sump­tion ­during an inpa­tient ­stay in ­acute ­care facil­ties (DRG ­system), in a reha­bil­i­ta­tion ­unit (FIM-FRG ­systems), or in a ­nursing ­home (RUG ­system). ­Each of ­these ­systems ­strives to ­keep ­some dis­tinc­tion ­across ­groups, ­based on clin­ical cri­teria, ­even ­when the dom­i­nant ­grouping cri­terion (e.g. ­cost homo­ge­neity) ­would ­rather sug­gest ­group ­merging. The ­main sta­tis­tical tech­nique ­adopted for ­case-mix ­grouping is the clas­sifi­ca­tion and regres­sion ­tree (­CART). ­CART ­allows to ­find the ­best com­pro­mise ­between the ­need to max­i­mise var­i­ance expla­na­tion of the depen­dent var­i­able (i.e. the homo­ge­neity cri­terion: clin­ical ­severity, ­cost, ­length of ­stay and the ­like), and the ­need to ­retain clin­i­cally iden­ti­fi­able dis­tinc­tions (e.g. ­based on the ­organ ­impaired). ­Using a clas­sifi­ca­tion ­system as a pay­ment ­system ­entails ­other con­straints: easi­ness of account­ability, dis­in­cen­tive ­against ­upcoding, dis­in­cen­tive ­against ­adverse selec­tion of ­more ­demanding ­patients. In reha­bil­i­ta­tion med­i­cine a FIM-FRG ­system is ­already ­adopted as a pay­ment ­system for ­post-­acute reha­bil­i­ta­tion in USA. ­Some ­trials on FIM-FRG clas­sifi­ca­tion ­have ­been suc­cess­fully com­pleted ­in ­Italy, too.