Validity and reliability of the German language SF-36 health survey in patients with amyotrophic lateral sclerosis
Pongratz D., Zierz S., Fischer W., Jenkinson C., Fitzpatrick R., Peto V., Swash M., Aarli JA., Burgunder JM., Evangelista T., Genthon R., Hardiman O., Illa I., Leigh PN., Ludin HP., Mazzini L., Meininger V., Mora JS., Ortega M., Papapetropoulos T., Pouget J., Robberecht W., Ronnevi LO., Sales-Luis M., Silani V., Wokke JHJ., Werdelin L.
Objectives: To evaluate response rate, data quality, score reliability and scaling assumptions of the 36 item Short Form Health Survey (SF-36) in a survey of Amyotrophic Lateral Sclerosis (ALS) patients recruited into the ALS Health Profile Study (ALS-HPS) in Germany. Design: A questionnaire based survey of patients diagnosed with ALS in Germany. Sample: Patients presenting at neurological clinics throughout Germany for treatment of their condition were asked to take part in the survey. Results: 355 patients were recruited, and responses were obtained from 291 (82.0%). Scores on six of the eight dimensions of the SF-36 showed high internal consistency. Energy/Vitality and General Health dimensions were the two exceptions. Items correlated more highly with their own (corrected) scale score than with other scale scores. However, on two dimensions (Role-Physical and Role-Emotional) there were high levels of missing data, and substantial floor and ceiling effects. The two factor model of underlying constructs of physical and emotional health for the SF-36 suggested by its developers was not supported in this patient group. Conclusion: The SF-36 appears to provide reliable information across most dimensions in ALS. In general, there were high levels of item completeness and a good spread of scores, but this was not true for the role functioning dimensions. The underlying two factor model for the SF-36 was not supported. The implications of these findings for measuring health status in this patient group are discussed.