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

bhongmakapat@yahoo.com

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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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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