OBJECTIVES: We set out to determine the psychometric validation of a 
disease-specific health related quality of life instrument for use in chronic 
rhinosinusitis, the 22 item Sinonasal Outcome Test (SNOT-22), a modification of 
a pre-existing instrument, the SNOT-20.
DESIGN, SETTING AND PARTICIPANTS: The National Comparative Audit of Surgery for 
Nasal Polyposis and Chronic Rhinosinusitis was a prospective cohort study 
collecting data on 3128 adult patients undergoing sinonasal surgery in 87 NHS 
hospitals in England and Wales. Data were collected preoperatively and at 3 
months after surgery, and analysed to determine validity of the SNOT-22. 
Test-retest reliability was assessed in a separate cohort of patients in a 
single centre.
MAIN OUTCOME MEASURES: The SNOT-22, a derivative of the SNOT-20 was the main 
outcome measure. Patients were also asked to report whether they felt better, 
the same or worse following surgery. To evaluate the SNOT-22, the internal 
consistency, responsiveness, known group differences and validity were analysed.
RESULTS: Preoperative SNOT-22 scores were completed by 2803 patients. 3-month 
postoperative SNOT-22 scores were available for 2284 patients of all patients 
who completed a preoperative form (81.5% response rate). The Cronbach's alpha 
scores for the SNOT-22 were 0.91 indicating high internal consistency. The 
test-retest reliability coefficient was 0.93, indicating high reliability of 
repeated measures. The SNOT-22 was able to discriminate between patients known 
to suffer with chronic rhinosinusitis and a group of healthy controls (P < 
0.0001, t = 85.3). It was also able to identify statistically significant 
differences in sub-groups of patients with chronic rhinosinusitis. There was a 
statistically significant (P < 0.0001, t = 39.94) decrease in patient reported 
SNOT-22 scores at 3 months. At 3 months the overall effect size in all patients 
was 0.81, which is considered large. We found the minimally important difference 
that is the smallest change in SNOT-22 score that can be detected by a patient, 
to be 8.9 points.
CONCLUSIONS: We have found the SNOT-22 to be valid and easy to use. It can be 
used to facilitate routine clinical practice to highlight the impact of chronic 
rhinosinusitis on the patient's quality of life, and may also be used to measure 
the outcome of surgical intervention. The minimally important difference allows 
us to interpret scores in a clinical context, and may help to improve patient 
selection for surgery.