Does the extended Glasgow Outcome Scale add value to the conventional Glasgow Outcome Scale?

Abstract

The Glasgow Outcome Scale (GOS) is firmly established as the primary outcome measure for use in Phase III trials of interventions in traumatic brain injury (TBI). However, the GOS has been criticized for its lack of sensitivity to detect small but clinically relevant changes in outcome. The Glasgow Outcome Scale-Extended (GOSE) potentially addresses this criticism, and in this study we estimate the efficiency gain associated with using the GOSE in place of the GOS in ordinal analysis of 6-month outcome. The study uses both simulation and the reanalysis of existing data from two completed TBI studies, one an observational cohort study and the other a randomized controlled trial. As expected, the results show that using an ordinal technique to analyze the GOS gives a substantial gain in efficiency relative to the conventional analysis, which collapses the GOS onto a binary scale (favorable versus unfavorable outcome). We also found that using the GOSE gave a modest but consistent increase in efficiency relative to the GOS in both studies, corresponding to a reduction in the required sample size of the order of 3-5%. We recommend that the GOSE be used in place of the GOS as the primary outcome measure in trials of TBI, with an appropriate ordinal approach being taken to the statistical analysis.

FIG. 1.

Numbers 1 to 4 on the horizontal axis correspond to following methods: 1, proportional odds, treatment only; 2, proportional odds, treatment+covariates; 3, sliding dichotomy, treatment only; and 4, sliding dichotomy, treatment+covariates. “Treatment only” means that the final analysis model contained the treatment variable only, while “Treatment+covariates” means that the final analysis model contained the treatment variable plus covariates (3 or 7). See the statistical analysis section for a list of the covariates used. GOS, Glasgow Outcome Scale; GOSE, Glasgow Outcome Scale-Extended.