• Eric C Parent, Doug Hill, Marc Moreau, Jim Mahood, Jim Raso, and Edmond Lou.
• Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, AB, Canada. eparent@ualberta.net
• Spine. 2007 Jul 15;32(16):1767-77.

Study DesignProspective cross-sectional measurement study.ObjectiveTo analyze the score distribution on the Scoliosis Quality of Life Index (SQLI) questionnaire domains and items for subjects with adolescent idiopathic scoliosis (AIS).Summary Of Background DataThe SQLI was derived from the SRS-22 questionnaire so that it would be more applicable to persons with AIS between 10 and 18 years old. However, the score distribution of the SRS-22 is characterized by high ceiling effects within subgroups of persons with AIS.MethodsThe SQLI questionnaire was completed by 95 females with AIS. Floor, ceiling effects, and score distribution were examined for subgroups based on age (n = 4), management (4), curve severity (3), and curve type (6).ResultsCeiling effect proportions (0%-40%) were higher than floor effects (n = 1). Back pain and satisfaction were the only domains with ceiling effects exceeding 20%. For some domains, ceiling effects were significantly most prevalent for younger subgroups, those with low or moderate curve severity and those treated less aggressively. High ceiling effects were also observed for the observation, postsurgical, main thoracic, and double major curves subgroups. More than half the participants scored over 4/5 for all SQLI domains in the overall sample and in the observation, surgery, <13.5 years, 13.5 to <15 years, <30 degrees, 30 degrees to 50 degrees, main thoracic curves, double major curves, and thoracolumbar/lumbar curves subgroups, respectively. At least one item from each domain (except satisfaction) showed ceiling effects >50% in most subgroups (14 or more subgroups out of 15).ConclusionEven though ceiling effects (>20%) were not common, scores clustered near the top of the SQLI scale. The SQLI score distribution may impair the questionnaire's sensitivity to change and discriminative ability, particularly in younger subjects with lesser low or moderate curve severity, under observation or after surgery. The clinical utility of some SQLI items within each domain may be limited by high ceiling effects.

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