Psychometric and clinimetric validity of the 20-Item
Sino-Nasal Outcome Test (SNOT-20)
JAY F. PICCIRILLO, MD, MICHAEL G. MERRITT, JR, BA, and MICHELE L. RICHARDS, MD, St. Louis, Missouri
A valid measure of rhinosinusitis health status and
quality of life is required for the complete assessment of treatment effectiveness. The purpose of this
study was to analyze the psychometric and clinimetric validity of the 20-Item Sino-Nasal Outcome
Test (SNOT-20), a disease-specific, health-related
quality-of-life measure for rhinosinusitis. The SNOT20 is a modification of the 31-Item Rhinosinusitis
Outcome Measure, and it contains 20 nose, sinus,
and general items. To complete the instrument,
patients indicate how much they are affected in
each area and identify the 5 most important items.
The SNOT-20 was completed by 102, 72, and 46
patients at the initial visit and at 6 months and 1
year after treatment commencement, respectively.
Cronbach’s α was 0.9; test-retest scores were highly correlated (r = 0.9). Patients who were more
affected had greater SNOT-20 scores (P < 0.002),
and patients who had improved had greater
change scores (P < 0.04). Items identified as important had greater scores (P < 0.0001) and showed
greater change scores (P < 0.0002). The SNOT-20 is
a valid outcome measure for patients with rhinosinusitis; it describes the health burden and is sensitive to clinical change. (Otolaryngol Head Neck
Surg 2002;126:41-7.)
R
hinosinusitis is the most commonly reported
chronic disorder in the United States, affecting
approximately 14% of the US population.1 Despite
From the Clinical Outcomes Research Office, Department of
Otolaryngology–Head and Neck Surgery, Washington University
School of Medicine. Dr Richards is currently affiliated with the
Department of Otolaryngology–Head and Neck Surgery,
University of Florida College of Medicine, Gainesville.
Presented at the Annual Meeting of the American Academy of
Otolaryngology–Head and Neck Surgery, San Antonio, TX,
September 13-16, 1998.
Reprint requests: Jay F. Piccirillo, MD, Department
of Otolaryngology–Head and Neck Surgery, 660 South Euclid
Ave, Box 8115, St. Louis, MO 63110; e-mail, piccirij@
msnotes.wustl.edu.
Copyright © 2002 by the American Academy of Otolaryngology
Head and Neck Surgery Foundation, Inc.
0194-5998/2002/$35.00 + 0 23/1/121022
doi:10.1067/mhn.2002.121022
this fact, the health burden of this disorder relative to
the general population and to other chronic diseases
has not been extensively evaluated. Recently, Gliklich
and Metson2 assessed the burden of this disorder by
using the Medical Outcomes Study Short-Form 36Item Health Survey (SF-36) 3 to compare data for
patients who underwent sinus surgery with normative
data derived from a sample of the general US population.4 Significant differences between these populations were seen in several domains, including bodily
pain, general health, vitality, and social functioning.
Comparisons with other chronic diseases revealed
significantly lower scores in measures of bodily pain
and social functioning for patients with rhinosinusitis
than for patients with congestive heart failure, angina,
chronic obstructive pulmonary disease, or back pain.
These findings suggest that the national health impact
of chronic rhinosinusitis is far greater than is currently appreciated.
Similar to the paucity of data on the health burden of
rhinosinusitis, little is known about the effects of treatments for rhinosinusitis. The evaluation of treatment is
presently impeded by a lack of valid instruments to
measure disease-specific health status and health-related quality of life (QOL). The incorporation of a valid
rhinosinusitis health status and QOL measure into the
reporting of outcomes after rhinosinusitis treatment will
allow for the standardization of outcomes and improvements in the precision, accuracy, and clinical relevance
of treatment evaluation.
The model of health status used by many researchers
for the development of disease-specific health status
measures is described according to the hierarchy outlined by the Institute for Medical Rehabilitation and
Research.5,6 In this model, health status can be
described by the physical impairments, functional limitations, disabilities, and societal limitations that a
patient experiences. The description of QOL, however,
is envisioned by the authors and others7-9 as existing
separately from the description of health status. QOL is
a uniquely personal experience that reflects not only
health status but also other factors and circumstances in
a patient’s life. According to this definition, physicians,
other health care professionals, and patients can
describe the health status of a patient, but only the individual patient can describe his or her QOL. Criteria for
the development and assessment of disease-specific
41
42
PICCIRILLO et al
QOL measures have been suggested by Guyatt et al10
and Guyatt and Cook.11
We report here on the development and validation of
the 20-Item Sino-Nasal Outcome Test (SNOT-20), a
disease-specific, health-related QOL measure. This
instrument is a modified version of the 31-Item
Rhinosinusitis Outcome Measure (RSOM-31).12
Patients describe their disease-specific health status by
indicating the severity of rhinosinusitis symptoms and
describe their QOL by indicating importance across different domains, including the physical problems, functional limitations, and emotional consequences of
rhinosinusitis. This instrument is intended primarily to
measure the effectiveness of treatment.
METHODS
Based on the validation work of the RSOM-31,12 2 modifications were made to create the SNOT-20. Eleven items
were removed for 2 reasons. First, a focus group of patients
and physicians believed that these items were redundant.
Second, based on psychometric analysis, these items did not
contribute significantly to the instrument. In addition to the
elimination of 11 items, the scoring of the SNOT-20 was
changed from that of the RSOM-31. It was determined that
calculation of the product of the magnitude and importance
scores greatly complicated the instrument scoring and did
not greatly contribute to the overall score. Therefore,
Instead of calculating the product of the magnitude and
importance scores, only the average magnitude score for the
20 items is calculated. However, the SNOT-20 does have an
importance rating. Patients are asked to indicate the 5 items
that are most important to them and that they expect to
improve with treatment.
The possible range of SNOT-20 scores is 0 to 5, with a
higher score indicating a greater rhinosinusitis-related health
burden. The impact of treatment is measured by calculating
the difference between SNOT-20 scores before and after treatment. Separate pretreatment, posttreatment, and change
scores can be calculated for the items selected at the initial
visit as being most important.
Population Under Study
Patients enrolled in the present study were part of the population of the Rhinosinusitis Outcomes Project, a prospective,
observational outcomes research project. The eligible population included all adult patients who presented with signs and
symptoms suggestive of rhinosinusitis to the Washington
University Department of Otolaryngology–Head and Neck
Surgery between February 1, 1995, and November 1, 1996.
Signs of rhinosinusitis included colored purulent nasal or
postnasal discharge and maxillary tooth tenderness to palpation. Symptoms included stuffy or blocked nose, runny nose,
facial pain or pressure, headache, cough, nasal obstruction,
Otolaryngology–
Head and Neck Surgery
January 2002
and fever. A trained research assistant provided eligible
patients with a packet that included demographic questions,
the SNOT-20, and a global disease-specific QOL rating question (“Please indicate the overall amount of disturbance or
‘bother’ that you experience in your life as a result of your rhinosinusitis problems” [responses included “Not bothered,”
“Bothered a little, but not much,” “Bothered more than a little,
but not a lot,” “Bothered a lot,” and “Extremely bothered”]).
This pretreatment period is referred to as the initial visit.
At approximately 6 months and 1 year after the initial visit,
patients were mailed the SNOT-20, the global disease-specific QOL rating question, and a treatment response question
(“Please describe your response to treatment over the past
week” [responses included “Much improved,” “Somewhat
improved,” “Neither improved nor worse,” “Somewhat
worse,” and “Much worse”]).
The SNOT-20 took approximately 10 minutes for patients
to complete. The Human Studies Committee approved this
project, and informed consent was obtained before inclusion
in the study.
Statistical Analysis: Psychometric and
Clinimetric Validity
To evaluate the SNOT-20, the internal consistency, reliability, and validity of the test were analyzed. The consistency
of the SNOT-20 was analyzed to determine whether the instrument was internally consistent. Internal consistency refers to
the way in which the items within an instrument relate to each
other. The statistical tests that were used to represent and evaluate internal consistency for ordinal responses are Cronbach’s
α,13 intercorrelations between questionnaire items, and item
correlations with the overall score. Reliability was analyzed
by retesting patients and correlating initial test and subsequent
retest scores.
To assess the ability of the SNOT-20 to measure rhinosinusitis-related QOL, 2 separate characteristics were explored:
construct validity and concurrent validity. Construct validity
refers to the degree to which rhinosinusitis-related QOL is
measured by an instrument and was determined by analyzing
content validity and discriminant validity.
The term content validity refers to the degree to which the
items in an instrument adequately reflect the content domain
being measured. An instrument that has content validity is free
from the influence of factors that are irrelevant to the purpose
of the measurement.14 To determine whether the SNOT-20 has
content validity, the process of its development was analyzed.
Discriminate validity was assessed through measurement of
the ability of the SNOT-20 to provide different results, or low
correlations, among 2 different groups of patients seeking care
at the Department of Otolaryngology–Head and Neck
Surgery: patients with rhinosinusitis and patients who sought
care for other conditions and did not have a clinical condition
suggestive of rhinosinusitis.
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43
Table 1. SNOT-20 initial visit, 6-month, and 1-year individual item and total instrument scores
Initial visit (n = 102)
Item
Mean
SD
Need to blow nose
Sneezing
Runny nose
Cough
Postnasal discharge
Thick nasal discharge
Ear fullness
Dizziness
Ear pain
Facial pain/pressure
Difficulty falling asleep
Wake up at night
Lack of a good night’s sleep
Wake up tired
Fatigue
Reduced productivity
Reduced concentration
Frustrated/restless/irritable
Sad
Embarrassed
SNOT-20 score
2.5
1.7
1.9
1.9
2.7
2.2
1.9
1.0
1.2
2.6
1.3
2.1
2.1
2.4
2.4
1.9
1.9
1.9
0.8
0.8
1.9
1.5
1.2
1.5
1.6
1.7
1.7
1.8
1.5
1.4
1.7
1.6
1.7
1.7
1.8
1.8
1.7
1.7
1.7
1.2
1.3
0.9
6 Months (n = 72)
Mean
1.8
1.1
1.2
1.0
2.2
1.8
1.3
0.6
0.6
1.2
1.2
1.9
1.8
1.9
1.8
1.3
1.4
1.4
0.8
0.7
1.3
SD
1.4
1.1
1.3
1.3
1.7
1.7
1.7
1.2
1.1
1.6
1.5
1.7
1.8
1.7
1.7
1.6
1.7
1.6
1.2
1.3
1.0
1 Year (n = 46)
Mean
1.8
1.4
1.3
1.2
2.0
1.5
1.4
0.7
0.5
1.3
1.2
1.8
1.8
2.3
2.0
1.7
1.6
1.5
0.8
0.7
1.4
SD
1.4
1.3
1.4
1.4
1.6
1.7
1.6
1.2
1.0
1.7
1.5
1.7
1.8
1.7
1.7
1.7
1.7
1.6
1.3
1.3
1.0
SNOT-20, 20-Item Sino-Nasal Outcome Test.
After the establishment of construct validity, concurrent
validity was assessed to determine the relationship between
the results of the SNOT-20 and standard criterion measures.
Patients’ responses to the global disease-specific QOL question formed the standard criterion against which the response
on the SNOT-20 was assessed.
The standardized response mean (SRM) was used to assess
the ability of the SNOT-20 change scores to measure the benefit of rhinosinusitis treatment. The SRM is defined as the
mean change score divided by its SD.15 In addition, SNOT-20
change scores were compared with the global treatment
response and satisfaction with medical care questions.
To determine the relevance of the items marked “important”
by patients at the time of their initial visit, the mean number of
items marked “important,” the mean item score for the important
items, and the mean SNOT-20 overall score were analyzed for
each follow-up interval. In addition, mean item change scores
for those items marked “important” and mean SNOT-20 change
scores were analyzed for each follow-up interval. The association of mean item change score for those items marked “important” and overall response to treatment was measured for the
6-month and 1-year follow-up periods.
All statistical analyses for this study were performed using
SAS, Version 6.12 (SAS Institute, Cary, NC). For the abovementioned analyses, t tests, analysis of variance, and
Pearson’s r were used where appropriate. A value of P < 0.05
was used to establish statistical significance.
RESULTS
The SNOT-20 and related questions were administered
to 102 patients who reported to the Washington University
Department of Otolaryngology–Head and Neck Surgery
with signs and symptoms of rhinosinusitis. The mean age
of this population was 49 years (range, 18.4 to 85.3 years),
and 72% were male. Of these 102 patients, 72 completed
the SNOT-20 approximately 6 months after the initial
visit, and 46 patients completed the SNOT-20 approximately 1 year after the initial visit.
The mean ± SD SNOT-20 score at the initial visit was
1.9 ± 0.9, and the mean ± SD 6-month and 1-year SNOT20 scores were 1.3 ± 1.0 and 1.4 ± 1.0, respectively.
The 5 items with the highest mean item scores at the
initial visit were postnasal discharge, facial pain/pressure, need to blow nose, wake up tired, and fatigue.
Internal Consistency
The overall Cronbach’s α was 0.90, suggesting good
internal consistency within the SNOT-20. The α coefficients for each item were 0.90. The correlation of each
item with the total SNOT-20 score was statistically significant for all 20 items (P < 0.001) (Table 1).
Test-Retest Reliability
A subset of 15 patients who completed the SNOT-20
at 1 year were mailed and completed the SNOT-20
44
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PICCIRILLO et al
Table 2. Association of mean SNOT-20 scores and overall affect at initial visit, 6 months, and 1 year
SNOT-20 score
Overall affect
Initial visit
Not bothered
Bothered a little, but not much
Bothered more than a little, but not a lot
Bothered a lot
Extremely bothered
Total
F = 4.8, P = 0.002
6 Months
Not bothered
Bothered a little, but not much
Bothered more than a little, but not a lot
Bothered a lot
Extremely bothered
Total
F = 20.2, P = 0.001
1 Year
Not bothered
Bothered a little, but not much
Bothered more than a little, but not a lot
Bothered a lot
Extremely bothered
Total
F = 11.7, P < 0.0001
n
Mean
SD
4
8
23
48
19
102
0.8
1.1
1.6
2.0
2.3
1.9
0.6
1.1
0.8
0.9
0.9
0.9
5
19
18
23
4
69
0.0
0.9
1.1
2.1
3.2
1.4
0.1
0.5
0.7
0.9
0.6
1.0
8
9
12
13
4
46
0.4
0.7
1.7
2.1
2.4
1.4
0.4
0.4
0.8
1.0
0.13
1.0
SNOT-20, 20-Item Sino-Nasal Outcome Test.
Three patients left this question blank.
approximately 2 and 4 weeks later. The mean difference
in SNOT-20 scores was 0.15 (t = 1.9, P = 0.08). Pearson
correlation analysis revealed a high degree of correlation between the scores at 2 and 4 weeks (r = 0.9,
P < 0.0001).
Content Validity
Each item of the SNOT-20 was developed from discussions with patients with rhinosinusitis using a semistructured interview, discussions with physicians, and a
review of the literature. The physical problems, functional limitations, and emotional consequences that
result from rhinosinusitis and its treatment were identified. Each of the 20 items of the instrument relates to
rhinosinusitis and the breadth of problems associated
with this condition.
Discriminant Validity
Ten people who said that they had no rhinosinusitisrelated problems were selected, and they completed the
SNOT-20. The mean SNOT-20 score was 0.6 for this
cohort, indicating very little problem with the 20 items
related to rhinosinusitis. The difference between the
mean values for the study cohort (1.9) and the 10 per-
sons who had no rhinosinusitis-related problems (0.6)
was statistically significant (P < 0.0001).
Concurrent Validity
Patients’ response to the global disease-specific QOL
(“overall bother”) question was compared with SNOT20 scores at each of the 3 time periods: initial visit, 6
months, and 1 year. The mean SNOT-20 scores were
calculated within each category of overall affect (Table
2). For each time interval, the mean SNOT-20 scores
increased significantly by category of overall affect
from “not bothered” to “extremely bothered” (initial
visit: F = 4.8, P = 0.002; 6 months: F = 20.2,
P < 0.0001; 1 year: F = 11.7, P < 0.0001).
SNOT-20 Sensitivity, Magnitude of Change, and
Clinically Meaningful Difference
Sensitivity to clinical change was assessed with the
SRM. The SRM was 0.4 at 6 months and 0.4 at 1 year.
These scores suggest that the SNOT-20 is moderately
sensitive to clinical change.
To validate the ability of the SNOT-20 to measure
change in patients’ rhinosinusitis symptoms, the SNOT20 change scores were compared with a global rating
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45
Table 3. Association between mean SNOT-20 change scores and treatment response
SNOT-20 change score
Response to treatment
6 Months*
Improved
Not improved or worse
Total
t = 2.2, P = 0.04
1 Year†
Improved
Not improved or worse
Total
t = –0.2, P = 0.8
n
Mean
SD
21
20
41
0.8
0.1
0.4
1.2
1.0
1.1
8
13
21
0.4
0.4
0.4
0.6
1.0
0.9
SNOT-20, 20-Item Sino-Nasal Outcome Test.
Twenty-one and 49 patients did not mark important items at the initial visit and at 6 months, respectively.
*Nineteen patients reported no treatment during the past week, 7 patients did not complete the SNOT-20 at initial visit, and 5 patients left this question blank.
†Eighteen patients reported no treatment during the past week, 5 patients did not complete the SNOT-20 at initial visit, and 2 patients left this question blank.
question of treatment response and overall satisfaction
with medical care for rhinosinusitis. Patients who indicated that their rhinosinusitis was improved at 6 months
had statistically significantly higher mean SNOT-20
change scores than did patients who had either not
improved or were worse (t = 2.2, P < 0.04) (Table 3). It
is interesting that patients who indicated their rhinosinusitis was improved at 1 year did not show a difference
in mean SNOT-20 change scores compared with those
who were not improved or were worse (t = –0.2, P = 0.8).
To estimate the amount of change on the SNOT-20
that is associated with a clinically meaningful difference, we analyzed the association of SNOT-20 change
scores and treatment response (Table 3). At 6 months,
patients who reported being improved had a mean
change score of 0.8, whereas patients who reported no
improvement or worse symptoms had a significantly
lower mean change score of 0.1. Based on these results,
a SNOT-20 change score of 0.8 or greater is believed to
be clinically meaningful.
Relevance of Items Marked “Important”
The 5 items most frequently reported as important at
initial visit were lack of a good night’s sleep, postnasal
discharge, wake up tired, fatigue, and thick nasal discharge. The mean SNOT-20 score for important items
was statistically significantly higher than mean SNOT20 scores overall at the initial visit (3.7 vs 2.0; t = 17.9,
P < 0.0001), 6 months (3.2 vs 1.8; t = 10.0, P <0.0001),
and 1 year (3.5 vs 1.8; t = 11.8, P < 0.0001), indicating
that items that are marked “important” are more severe.
The mean SNOT-20 change scores for important items
were statistically significantly higher than the mean
SNOT-20 change scores overall at 6 months (1.1 vs 0.5;
t = 4.5, P < 0.0001) and 1 year (1.3 vs 0.4; t = 4.3,
P = 0.0002), indicating that patients reported greater
improvement for important items. The SRM for the
mean SNOT-20 change scores for important items was
0.625 at 6 months and 0.73 at 1 year. The mean SNOT20 change scores at 6 months and 1 year for items
marked “important” at the initial visit were also compared with results for the global question of treatment
response. Patients who showed improvement had statistically significantly higher SNOT-20 change scores for
important items at the initial visit than did those who
showed no improvement or were worse at 6 months (1.7
vs 0.2 vs 0.7; F = 4.3, P = 0.02). The differences in
mean SNOT-20 scores at 1 year were not statistically
significant (0.8 vs 1.0 vs 2.2; F = 0.9, P = 0.43).
DISCUSSION
In this study, the SNOT-20 is demonstrated to be a
valid disease-specific health-related QOL measure for
patients with rhinosinusitis. There are 3 unique aspects
to the SNOT-20. First, the items were derived from a
valid measure (RSOM-31) and from discussions with
patients who report having rhinosinusitis. Second, the
SNOT-20 includes a small, yet wide, range of items that
are important to patients with rhinosinusitis. Third, the
SNOT-20 allows patients to indicate which items are
most important to them, independent of the magnitude
of the problem. We believe that this last feature makes
the SNOT-20 both a health status measure and a QOL
measure. Although the important items are not weighted or directly used in the scoring of the SNOT-20, it has
been demonstrated that the mean magnitude score is
higher for the important items and that patients show
greater improvement in important items. In addition, it
46
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PICCIRILLO et al
has been shown that change scores of important items
are significantly associated with treatment response,
and the SRM is higher for the items marked “important.” Because of this, we believe that a patient’s indication of importance provides information that helps the
physician focus his or her treatment and is vital to the
description of QOL for both research and clinical purposes.
A potential weakness of this study deserves mention.
In analysis of the response to treatment, there was no
significant difference in mean SNOT-20 change scores
at 1 year from initial visit. To assess clinical improvement and SNOT-20 change scores, patients were asked
to describe their response to treatment during the past
week. Because patients were readministered the SNOT20 at 6-month intervals, it might have been better to ask
either about treatment response in general or about the
response over a longer period than 1 week (eg, during
the past month). We believe that if the question were
asked differently, the responses would more closely
match the change in rhinosinusitis and related symptoms that is assessed by the SNOT-20 at 6 months.
There are several other validated rhinosinusitis outcome measures available for routine use in clinical
practice and research.16 The Rhinosinusitis Quality of
Life Questionnaire17 is a self-administered instrument
that describes symptoms in 7 domains: sleep, non–hay
fever symptoms, practical problems, nasal symptoms,
eye symptoms, activities, and emotional function. The
instrument takes 5 to 10 minutes to complete and is
intended to be used repeatedly over time for longitudinal assessment. The Chronic Sinusitis Survey18 is a 6item duration-based monitor of sinusitis-specific
outcomes that has a symptom-based section and a medication-based section. In the symptom-based section,
the patient answers questions concerning the duration
of sinus headaches/facial pain or pressure, nasal discharge, and nasal congestion or obstruction. The medications assessed include oral antibiotics, prescription
nasal sprays, and over-the-counter sinus medications.
The 2 section subscores and a total score are calculated
and normalized by a scale of 0 to 100, with 0 being the
worst possible score and 100 being the best possible
score. The Symptom Score Instrument19 is a 5-symptom (facial pain or pressure, headache, nasal blockage
or congestion, nasal discharge, and olfactory disturbance) visual analog scale. The patient also ranks the 3
worst symptoms, clarifying the patient’s priorities. In
the Rhinosinusitis Disability Index,20 the patient is
asked to relate nasal and sinus symptoms to specific
limitations in daily functioning. All of these instruments
are valid, and the use of any particular instrument
should be guided by the goals of the application.
The SNOT-20 is easy for patients to complete and
can be used in routine clinical practice to inform clinicians about a full range of problems associated with rhinosinusitis. Responses on the instrument can help focus
the clinical encounter. The SNOT-20 change score can
be combined with other outcome measures, such as satisfaction and cost of care, to measure effects over time
and to provide a more complete description of outcome.
The SNOT-20 can also aid researchers in assessing the
degree and effect of rhinosinusitis on health status,
QOL, and measure treatment response. When suitable
severity of disease and outcome measures are used,
treatment effectiveness can be assessed.21 Once rhinosinusitis treatment effectiveness can be measured,
research can be conducted to identify patient factors
that predict the greatest treatment response.
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