Abstract
IMPORTANCE: Patient-reported measures are designed to detect a true change in outcome, but they are also subject to change from biases inherent to self-reporting: changing internal standards, changing priorities, and changing interpretations of a given instrument. These biases are collectively known as "response shifts" and can obscure true change after medical interventions. OBJECTIVE: To determine the presence of response shifts in patients with chronic rhinosinusitis (CRS) after endoscopic sinus surgery. DESIGN, SETTING, AND PARTICIPANTS: Multisite, prospective, observational cohort study conducted at academic tertiary care centers between February 2011 and May 2013. Study participants comprised a population-based sample of 514 adults (age ≥18 years) with CRS, who elected surgical intervention for continuing medically refractory symptoms. INTERVENTION: Endoscopic sinus surgery. MAIN OUTCOMES AND MEASURES: Preoperative and postoperative data from the 22-item Sinonasal Outcome Test (SNOT-22) survey instrument was characterized using exploratory factor analysis. Subsequent longitudinal structural equation models were estimated to test structure, potential response shifts, and true change in the SNOT-22 scores. RESULTS: A total of 339 participants (66.0%) provided survey evaluations at baseline and 6-month follow-up. Factor analysis of the SNOT-22 revealed 5 correlated, yet distinguishable, underlying factors. Endoscopic sinus surgery had a differential impact across these factors, with the largest effect size in rhinologic symptoms (mean [SD] SNOT-22 scores before and after surgery, 13.18 [5.11] and 7.37 [5.48], respectively; d = -1.13 [P < .001]) and extranasal rhinologic symptoms (8.31 [3.46] and 4.83 [3.68], respectively; d = -1.00 [P < .05]) (d is an effect size measure defined as the difference in means divided by the presurgery SD). Endoscopic sinus surgery had a smaller, yet significant, effect size on the remaining 3 factors: ear/facial symptoms (7.32 [4.6]) and 3.90 [4.07], respectively; d = -0.74 [P < .001]), psychological dysfunction (11.90 [7.21] and 6.50 [6.69], respectively; d = -0.75 [P < .05]), and sleep dysfunction (10.12 [5.59] and 5.88 [5.37], respectively; d = -0.76 [P < .001]). Participants were found to undergo recalibration, reprioritization, and reconceptualization of symptoms after intervention; however, the magnitude of these response shifts was small and not clinically significant. CONCLUSIONS AND RELEVANCE: The SNOT-22 measures 5 distinct factors, not a single construct. Reporting of individual subscale scores may improve sensitivity of this instrument in future studies. Participants undergoing endoscopic sinus surgery experience only clinically insignificant response shifts, validating assessment of change through use of presurgery and postsurgery SNOT-22 responses. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT01332136.