Development and validation of the Glasgow epilepsy outcome scale (GEOS): Anew instrument for measuring concerns about epilepsy in people with mentalretardation

Purpose: To develop a measure For use with adults with epilepsy and mental retardation, capable of assessing both clinical and care concerns and of qu antifying treatment outcomes. Methods: Extensive validational and other psychometric evaluation was under taken, comprising initial scale development work with 48 carers and 46 heal th practitioners, followed by formal field testing on a sample of 186 patie nts, using 384 respondents (160 clinicians, 141 staff, 83 family). Recognis ed qualitative methods were applied to identify central themes. and psychom etric procedures generated data on validity, reliability, and component str ucture. Results: A total of 1,007 items of concern was generated. which was reduced systematically to a representative set of 90 items. The GEOS-90 comprises four subscales: concerns about "seizures," "treatment," "caring," and "soci al impact," each explaining similar to 70% of variance. Subscales and facto r scales had strong internal consistency (alpha greater than or equal to 0. 82). Stepwise linear regression was applied to derive a short-form version with similar structure. Thirty-five items were retained (GEOS-35; alpha gre ater than or equal to 0.89). Both scales discriminated moderately on clinic al variables (number of seizure types, mono- vs. polytherapy, seizure frequ ency; all values of p < 0.05) and demonstrated concurrent validity with int erview ratings from the ELDQOL (p < 0.05), Conclusions: The GEOS scales appear valid and reliable for use with clinica l populations of people with mental retardation.