Validity, Reliability, and Responsiveness of SRS-7 as an Outcomes Assessment Instrument for Operatively Treated Patients With Adult Spinal Deformity

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Abstract

Study Design.

A retrospective analysis.

Objective.

The aim of our study was to compare the normality, concurrent validity, internal consistency, responsiveness, and dimensionality of an item response theory–derived seven-question instrument (SRS-7), against the Scoliosis Research Society-22r (SRS-22r) questionnaire in operatively treated patients with adult spinal deformity (ASD).

Summary of Background Data.

Compared with SRS-22r, SRS-7 (which has been validated in operatively treated patients with adolescent idiopathic scoliosis) has advantages of being short, unidimensional, and linear.

Methods.

A prospective database of ASD patients was queried for patients 18 years or older who were operatively treated, and who answered pre- and postoperative (at 2-year follow-up) SRS-22r questions (n = 276). Corresponding SRS-7 scores were calculated using answers to SRS-22r items 1, 4, 6, 10, 18, 19, and 20. Significance was set at a P value less than 0.01.

Results.

SRS-7 and SRS-22r were normally distributed preoperatively but not postoperatively. SRS-7 and SRS-22r scores had high correlation both preoperatively (r = 0.76, P < 0.01) and postoperatively (r = 0.83, P < 0.01). The internal consistency reliability Cronbach α values were 0.61 (SRS-7) and 0.83 (SRS-22r) preoperatively and 0.91 (SRS-7) and 0.95 (SRS-22r) postoperatively. SRS-7 was found to be more responsive than SRS-22r with measures of effect size: Cohen d = 1.21 versus 1.13, Hedge g = 1.21 versus 1.13, and effect size correlation r = 0.52 versus 0.49. Iterative principal factor analysis of pre- and postoperative scores showed the presence of one dominant latent factor in SRS-7 (unidimensionality) and four latent factors in SRS-22r (multidimensionality).

Conclusion.

SRS-7 is a valid, reliable, responsive, and unidimensional instrument, which can be used as a short-form alternative to the SRS-22r for assessing global changes in patient-reported outcomes over time in patients with ASD.

Conclusion.

Level of Evidence: 3

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