The Oswestry Disability Index is not a good measure for low back pain in adolescents: A Rasch analysis of data from 200 people.

Objective: To evaluate the psychometric properties of the modified Oswestry Disability Index in adolescents with low back pain through Rasch analysis.

Design: This is a psychometric study.

Setting: Physical therapy clinics of a large pediatric hospital in Columbus, Ohio (United States).

Subjects: Two hundred adolescent patients with low back pain (112 female, 15.4 ± 1.9 years old).

Main measure: The modified Oswestry Disability Index.

Results: The mean modified Oswestry Disability Index score was 17.1 ± 12.1, with scores ranging from 0 to 56 on the 100-point scale. The Rasch person reliability for the Oswestry Disability Index was 0.70, representing minimal acceptable person reliability. The Oswestry Disability Index demonstrated poor item spacing, hierarchy, and targeting of the adolescents' disability level (>1 logit between person mean and item mean). A significant misfit was observed in three of 10 items. There were significant issues with the functioning of responses on all items of the Oswestry Disability Index. Principal component analysis of residuals revealed a ratio of 5.3:1, demonstrating acceptable unidimensionality.

Conclusion: Due to multiple psychometric issues, the Oswestry Disability should not be used to assess disability in adolescents with low back pain. The Oswestry Disability Index significantly mistargets adolescent ability and only provides an acceptable assessment of the most disabled adolescents.