RHINOLOGY
The validity and reliability of Thai Sinonasal Outcome Test-22
Pawin Numthavaj1 • Thongchai Bhongmakapat2 • Boonsarm Roongpuwabaht2 •
Atiporn Ingsathit1 • Ammarin Thakkinstian1
Received: 24 March 2016 / Accepted: 27 July 2016
� Springer-Verlag Berlin Heidelberg 2016
Abstract Chronic rhinosinusitis (CRS) symptoms can
significantly reduce quality of life. The Sinonasal Outcome
Test-22 (SNOT-22) is frequently used to assess this dis-
ease-specific quality of life, although it has not been
translated into Thai language. We translated the original
SNOT-22 questionnaire to Thai using forward–backward
technique, and validated it in CRS patients [n = 229, mean
age of 52.6 (SD = 15.9)] recruited at outpatient Oto-
laryngology clinic, Faculty of Medicine Ramathibodi
Hospital, Bangkok, Thailand. A construct validity was
assessed using factor analysis, reliability was assessed
using intra-class correlation coefficient (ICC) after 3 days
of taking the first questionnaire, and internal consistency
was assessed using Cronbach’s alpha. A total of 201 out of
229 patients completed SNOT-22 questionnaire. Factor
analysis with oblique rotation was applied and yielded
three domains with eigenvalue of 1 or higher. These
domains were named as nasal-related, ear–general–psy-
chological, and sleep-related domains. Estimated ICC
ranged from 0.49 to 0.71 with a median of 0.64, and
Cronbach’s alpha was 0.94. The Thai SNOT-22 question-
naire is reliable and valid with three domains. Thai SNOT-
22 may be used in research and clinical practice to assess
disease-specific quality of life and aid in management plan
at CRS clinic.
Keywords Validity � Reliability � Questionnaire � Chronicrhinosinusitis � Outcome � Sinonasal Outcome Test
Introduction
Chronic rhinosinusitis (CRS), an inflammatory disorder of
the nose and paranasal sinus, is estimated to be the second
most prevalent chronic health condition affecting approx-
imately 31 million/year in the US [1]. CRS is defined as
having at least two of following symptoms: anterior or
posterior nasal discharge, nasal obstruction, facial pres-
sure/pain, and reduced sense of smell lasting for more than
3 months. Diagnosis is based on symptoms above and
positive findings of polyp, discharge, or edema/obstruction
upon nasal endoscopy and/or mucosal changes from com-
puterized tomography imaging [2–4].
Symptoms of CRS such as chronic nasal congestion,
facial pressure or pain, headache, hyposmia, and anosmia
can significantly reduce quality of life (QOL) [5]. Man-
agement, therefore, mainly aims to reduce its symptoms
and thus improve QOL. Several questionnaires have been
used to assess this disease-specific QOL [6], and the
Sinonasal Outcome Test-22 (SNOT 22) is one among those
which is frequently applied [7]. It was originally developed
in 1998, which consisted of 16 items [8], and then was later
modified to be 20 items, and finally 22 items [9]. The
questionnaire had been tested and showed high reliability
and validity, and significantly correlated with general QOL
measured by the SF-36 [8]. In addition, the SNOT-22 has
been translated to other languages worldwide including
Electronic supplementary material The online version of thisarticle (doi:10.1007/s00405-016-4234-8) contains supplementarymaterial, which is available to authorized users.
& Thongchai Bhongmakapat
1 Section for Clinical Epidemiology and Biostatistics, Faculty
of Medicine Ramathibodi Hospital, Mahidol University,
Bangkok, Thailand
2 Department of Otolaryngology, Faculty of Medicine
Ramathibodi Hospital, 270 Rama VI Road, Ratchathewi,
Bangkok 10400, Thailand
123
Eur Arch Otorhinolaryngol
DOI 10.1007/s00405-016-4234-8
Chinese [10], French [11], Czech [12], Greek [13], Swed-
ish [14], Danish [15], Spanish [16], European Portuguese
[17], Brazilian Portuguese [18], Persian [19], Lithuanian
[20], and Turkish [21] but not yet for Thai language. We,
therefore, conducted the cross-sectional study which aimed
to translate and test the Thai SNOT-22 questionnaire.
Materials and methods
This study was a cross-sectional study which was con-
ducted during the 1 May 2014 to 20 January 2015 at the
outpatient Otolaryngology clinic, Faculty of Medicine,
Ramathibodi Hospital, Bangkok, Thailand. Ramathibodi
Hospital is a tertiary care hospital with an estimated
number of outpatient visits at otolaryngology department
around 90,000 visits per year. Patients presented with signs
and symptoms of CRS mentioned previously were asked
for participation. Patients were diagnosed, based on the
European position paper on rhinosinusitis and nasal polyps
(EPOS) 2012 [3], as CRS if they had at least one symptom
within a period of 12 weeks or longer (i.e., nasal blockage/
obstruction/congestion) plus one or more of the following:
nasal discharge (anterior/posterior nasal drip), facial
pain/pressure, and reduction/loss of smell. Diagnoses were
confirmed by physical examination, diagnostic rigid nasal
endoscopy with or without computerized tomography (CT)
of paranasal sinus.
Patients were eligible to join the study if they were
18 years or older, had bilateral CRS, were able to com-
municate well in Thai language with a degree of at least
primary school (equivalent to grade 6), had good con-
sciousness, willing to participate and provided consent
forms. We excluded patients with diagnosis of sinonasal,
nasopharyngeal, or other respiratory tract tumour and
malignancy.
Translation of SNOT-22 questionnaire
The SNOT-22 consisted of six domains, i.e., rhinological,
sleep, ear/facial, general, physical and psychological
domains. These corresponded domains consisted of 6, 4, 3,
5, 1, and 3 questions, and each question was graded using
Likert scale from no problem (0) to problem as bad as it
can be (5).
We had first contacted the corresponding author of the
original SNOT-22 questionnaire (PFJ) to request for per-
mission before translation. The modified forward–back-
ward technique of translation of questionnaire,
recommended by the European Organization for Research
and Treatment of Cancer approach [22], was applied as
following steps: first, the SNOT-22 questionnaire was
translated from English to Thai by Thai professional
translator who was not familiar with the questionnaire and
did not have knowledge of technical/medical terminology.
This translation was aimed to make simple language for
general Thai people. Then, the subsequent Thai version
was translated back to English by another independent
professional translator, who had never been exposed to the
original SNOT-22 questionnaire. Finally, the translated
English version was compared to the original version by
two native English speakers for inconsistencies.
All reports of translations were then reviewed by our
research team. Discrepancies were explored for errors of
translation and solved by consensus. Finally, the Thai
version was again revised accordingly to make the trans-
lated English and original versions as similar as possible.
Data collection
As for a rule of thumb for questionnaire validation, a
sample of around 10 patients per question was required
[23], resulting in 220 patients in total. The study was
approved by the Institutional Review Board of the Faculty
of Medicine, Ramathibodi Hospital (EC ID 02-57-29).
Data collection was performed at the outpatient Otolaryn-
gology clinic. CRS patients were approached by research
nurses to assess for eligibility and invite patients to par-
ticipate with the study. After giving consents, patients were
firstly asked to do a self-administered Thai SNOT-22
questionnaire in a private room. They could ask for an
explanation from a researcher assistant if they did not
clearly understand the questions. To assess reliability,
patients were 3 days later reminded by our researcher to
repeatedly do the Thai SNOT-22 questionnaire at home,
and posted it back to our centre. With this relatively short
time interval it should not change the disease condition.
Data analysis
Continuous data were described using mean and standard
deviation (SD), or median and range if the distribution of
data were not normal. Categorical data were described
using frequency and percentages.
Factor analysis was used to assess construct validity of
the Thai SNOT-22. Twenty-two questions were fitted in the
factor analysis model. An oblique rotation was applied
because there may be correlations among domains. Factor
domains with eigenvalue of 1 or higher were kept. Each
question was judged to belong to that factor domain if its
factor loading was three or higher. If a question was loaded
on more than one factor domain, that question was con-
sidered to belong to the factor domain with higher factor
loading, or more consistent with the original domain.
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123
Reliability was assessed using test–retest and internal
consistency. Test–retest, measured repeatability over time,
was assessed using intra-class correlation coefficient (ICC),
which ranged from 0 to 1. An ICC of at least 0.6 to\0.8 is
considered as good repeatability, whereas the value of 0.8
or higher is considered as excellent repeatability [24].
Cronbach’s alpha, which measures homogeneity and ran-
ges from 0 to 1, was estimated to assess internal consis-
tency. Higher value reflects higher consistency/
homogeneity, in which a value of C0.8 is acceptable as
good internal consistency [24]. All analyses were per-
formed using STATA 14.0.
Results
A total number of 244 patients were recruited during the
period of study but 15 patients were excluded (2 patients
duration of symptom\12 weeks, 13 patients had unilateral
CRS), and the remaining 229 patients were eligible for
analysis.
Baseline characteristic of patients were shown in
Table 1. One hundred and ten patients were male (48.0 %).
Mean age and BMI were 52.6 (SD = 15.9) years and 24.6
(SD = 4.4) kg/m2 with a median of symptom duration of
5 years (range 3 months to 63 years). Most patients were
married (58.5 %), about one third graduated bachelor’s
degree, and about 43.2 % were governmental employees.
A total of 87 (38 %) patients had prior surgery, about a half
of patients reported allergic rhinitis (133 patients, 58.1 %)
and nasal polyposis (113 patients, 49.3 %). Diabetes was
prevalent about 11.4 % but hypertension was more com-
mon with a prevalence of 32.3 %.
Data for each of 22 questions was described in supple-
ment Table 1. Among 229 patients, 28 patients did not
completely answer all questions, leaving 201 patients for a
complete-case analysis. A total SNOT-22 score ranged
from 2 to 102 with a mean of 38.15 (SD = 21.45).
For the follow up questionnaire, 208 patients returned
questionnaires at day 3, which resulted in a response rate of
90.83 %. Among them, 36 (17.3 %) patients did not
complete all 22 questions, or at least 1 question was
missing, leaving 172 for assessing reliability.
Validity
Factor analysis was performed to assess construct validity
of the Thai SNOT-22. An oblique rotation yielded only
three domains that had eigenvalue 1 or higher. Factor
loading was estimated for each question, and this was
displayed in Table 2 along with original belonging
domains.
Considering based on factor loading of 0.3 or higher, the
first factor domain consisted of 8 questions with factor
loadings which ranged from 0.36 to 0.84. Six (question 2
sneezing, question 3 runny nose, question 5 post-nasal
discharge, question 6 thick nasal discharge, question 21
sense of smell or taste, and question 22 blockage/conges-
tion of nose), 1 (question 1 need to blow nose), and 1
(question 4 cough) originally belonged to rhinological
domain, physical domain, and general domain, respec-
tively. This factor was re-named as nasal-related domain.
The second domain consisted of 10 questions, with
factor loading which ranged from 0.41 to 0.84. Among
these questions, 3 (question 7 ear fullness, question 8
dizziness, and question 9 ear pain), 4 (question 10 facial
pain/pressure, question 15 fatigue, question 16 reduced
productivity, and question 17 reduced concentration), and 3
(question 18 frustrated/restless/irritable, question 19 sad,
and question 20 embarrassed) questions originally belon-
Table 1 Baseline characteristics of study participants
Characteristics n = 229
Age, years, mean (SD) 52.6 (15.9)
Sex—male, n (%) 110 (48.0 %)
Body mass index, kg/m2, mean (SD) 24.6 (4.4)
Marital status, n (%)
Single 66 (28.8 %)
Married 134 (58.5 %)
Widowed 29 (12.7 %)
Education, n (%)
Primary school 49 (21.4 %)
Secondary school or vocational certificate 80 (34.9 %)
Bachelor’s degree or higher 98 (42.8 %)
Income per month, baht
No income 43 (18.8 %)
\10,000 29 (12.7 %)
10,001–15,000 24 (10.5 %)
15,001–30,000 81 (35.4 %)
30,001–50,000 22 (9.6 %)
50,001–100,000 23 (10.0 %)
C100,000 4 (1.8 %)
Not specified 3 (1.3 %)
Underlying disease, n (%)
Hypertension 74 (32.3 %)
Diabetes 26 (11.4 %)
Heart disease 19 (8.3 %)
Duration of nasal symptom, months, median (range) 60 (3–756)
History of sinonasal surgery, n (%) 87 (38.0 %)
History of allergic rhinitis, n (%) 133 (58.1 %)
History of nasal polyposis, n (%) 113 (49.3 %)
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ged to the ear/facial domain, general domain, and psy-
chological domain, respectively. This factor was re-named
as ear–general–psychological domain.
The last domain contained 4 questions (i.e., question 11
difficulty falling asleep, question 12 waking up at night,
question 13 lack of a good night’s sleep, and question 14
wake up tired), in which they were all originally belonged
to sleep domain. The factor loading of this factor ranged
from 0.49 to 0.81. This factor was re-named as sleep-re-
lated domain.
Reliability
The test–retest reliability, which measured repeatability, of
the Thai SNOT-22 was assessed by estimating ICC, see
Table 3. The results indicated that the estimated ICC ran-
ged from 0.49 to 0.71 with a median of 0.64, where the
minimum and maximum ICCs were, respectively, question
2: sneezing and question 13: lack of good night’s sleep. A
total of 17 (77 %) out of 22 questions had ICC of 0.60 or
higher.
In addition, Cronbach’s alpha was also estimated to
assess internal consistency of the first administered ques-
tionnaire, which yielded high internal consistency with the
estimated Cronbach’s alpha of 0.94.
Discussion
We performed a translation of the SNOT-22 questionnaire
into Thai language using a method of forward–backward
translation. Assessing construct validity indicated that the
Thai SNOT-22 consisted of three domains, instead of six
domains as the original version, which were ear–general–
psychological, nasal-related, and sleep-related domains.
These new domains consisted of 10, 8, and 4 questions,
respectively. In addition, the Thai SNOT-22 was reliable
with acceptable ICC and good internal consistency.
Table 2 Factor analysis
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The SNOT-22 questionnaire is easy to understand and
should be comprehensible by patients who were educated
to at least primary school or higher. It is also easy for
clinician to apply in a routine clinical practice to assess
disease conditions. The questionnaire was highly reliable
with Cronbach’s alpha of 0.91 [9] for the original version.
This was consistent with our Thai version, and also other
languages’ versions such as French [11], Czech [12], Greek
[13], Swedish [14], Danish [15], Spanish [16], European
Portuguese [17], Brazilian Portuguese [18], Persian [19],
Lithuanian [20], and Turkish [21] with Cronbach’s alpha of
0.93, 0.85, 0.84, 0.91, 0.83, 0.91, 0.94, 0.93, 0.90, 0.89,
0.88, respectively (see Supplement Table 2). In addition,
the test–retest reliability was average in good level for Thai
version, with 77 % of questions had ICC of 0.6 or higher.
This was comparable to the Spanish version which reported
overall ICC of 0.87 and average ICC of 0.71.
As for our knowledge, only our study assessed construct
validity after questionnaire translation. The Thai SNOT-22
could identify only three domains (i.e., nasal-related nasal,
ear–general–psychological, and sleep-related domains)
instead of six domains in the original version. These three
new domains consisted of 10, 8, and 4 questions, respec-
tively. For nasal-related domain, all questions in the original
rhinological domain were still kept in this new domain plus
two questions, one fromphysical domain (question 1: need to
blow nose) and another from general domain (question 4:
cough). Actually, these two questions can be thought as
symptoms. Therefore, Thai patients may not be able to dis-
tinguish and consider these symptoms to be similar to other
aspects of nasal symptom. Also, these two questions were
very much related with rhinological symptoms, and thus we
named the new domain as nasal related domain.
For ear–general–psychological, all questions in the orig-
inal ear, general, and psychological domains were kept,
except the question 4: cough, and combined into one domain.
This could reflect that Thai patients usually consider other
symptoms that were not the nose’s problems as related
symptoms apart from the nasal problem. Therefore, we
named this domain as ear–general–psychological domain.
For the sleep domain, all questions in the original sleep
domain were still kept, which indicated that Thai people
consider and distinguish sleep problem as another problem
separately from the other domains.
However, we also have minor limitation. We had planned
for sample size using a rule of thumbof 10 subjects per one item
of questionnaire, butwefinally came up 201 out of 220 subjects
with a subject to item ratio of 9.14. This should not very much
affect testing the construct validity by having looked at SNOT-
22 distribution, which was still normal distribution. Although
only 172 subjects were available for repeating questionnaires,
this should be adequate for testing reliability.
The Thai SNOT-22 score should be able to apply in
clinical practice and further research to assess the disease-
Table 3 Describe intra-class
correlation coefficient of the
test–retest reliability
Item Description Original domain ICC 95 % CI
1 Need to blow nose Physical 0.51 0.39–0.60
2 Sneezing Rhinological 0.49 0.37–0.59
3 Runny nose Rhinological 0.53 0.42–0.62
4 Cough General 0.59 0.49–0.68
5 Post nasal discharge (dripping at the back of your nose) Rhinological 0.69 0.61–0.76
6 Thick nasal discharge Rhinological 0.60 0.49–0.69
7 Ear fullness Ear/facial 0.69 0.61–0.76
8 Dizziness Ear/facial 0.69 0.60–0.76
9 Ear pain Ear/facial 0.67 0.58–0.74
10 Facial pain/pressure General 0.70 0.62–0.77
11 Difficulty falling asleep Sleep 0.64 0.55–0.72
12 Waking up at night Sleep 0.67 0.58–0.74
13 Lack of a good night’s sleep Sleep 0.71 0.63–0.78
14 Waking up tired Sleep 0.64 0.55–0.72
15 Fatigue General 0.64 0.54–0.71
16 Reduced productivity General 0.64 0.55–0.72
17 Reduced concentration General 0.60 0.49–0.68
18 Frustrated/restless/irritable Psychological 0.60 0.50–0.68
19 Sad Psychological 0.60 0.49–0.68
20 Embarrassed Psychological 0.59 0.48–0.67
21 Sense of taste/smell Rhinological 0.70 0.62–0.77
22 Blockage/congestion of nose Rhinological 0.61 0.51–0.70
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specific quality of life in CRS patients. Patients with higher
scores should have more disease symptoms and thus poor
quality of life when compare to patients with lower score.
The score should also use to assess disease progression,
i.e., improvement or worsening by comparing the score
measuring before and after receiving the intervention. A
minimal clinical important difference is subjective and
varied based on clinicians’ experiences. For instance, the
previous study defined score improvement if it reduced
about 8.9 from 110 baseline scores [9].
Conclusion
The Thai SNOT-22 questionnaire is valid and reliable in
Thai CRS patients. Factor analysis of the translated ques-
tionnaire yielded three domains instead of original six
domains. Thai SNOT-22 may be used in research and
clinical practice to assess disease-specific quality of life
and aid in management plan at CRS clinic.
Main findings and implications
Thai translated version of SNOT-22 is a valid, reliable and
easy to use in Thai CRS patients. While some domain from
factor analysis would have to re-group, factor analysis
could retain all questions in the questionnaire.
Implications for further study
Thai translated version of SNOT-22 could be use in Thai
CRS patients for further studies.
Acknowledgments This manuscript is an important part of the
training of Dr. Pawin Numthavaj who is a Ph.D. student in Clinical
Epidemiology in the Faculty of Medicine Ramathibodi Hospital,
Mahidol University, Bangkok Thailand. We thank Mr. Stephen Pin-
der, Mr. Neill deHaan, and Mrs. Pornpayong Numthavaj Koga for the
translation of SNOT-22 questionnaire.
Compliance with ethical standards
Funding This study was funded by Mahidol University.
Conflict of interest The authors declare that they have no conflict of
interest.
Research involving human participants All procedures performed
in this study were in accordance with ethical standards of institutional
and/or national research committee and with the 1964 Helsinki dec-
laration and its later amendments or comparable ethical standards
(Faculty of Medicine Ramathibodi Hospital Ethical Clearance No.
MURA2014/95).
Informed consent Informed consent was obtained from all individ-
ual participants included in the study.
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