Online Supplement Validation of the English Severe Respiratory Insufficiency Questionnaire METHODS

Online Supplement
Validation of the English Severe Respiratory Insufficiency Questionnaire
Dipansu Ghosh, Peter Rzehak, Mark W Elliott , Wolfram Windisch
METHODS
Study Design and Population:
This cross-sectional study was conducted in the Department of Respiratory Medicine at St.
James’ University Hospital, Leeds, UK, a tertiary care teaching hospital. Ethical approval was
obtained from local National Health Service (NHS) Ethics Committee.
Patients with chronic hypercapnic respiratory failure from a wide variety of causes
established on HMV for at least one month were eligible for the study. They had to be in a
clinically stable state, without any changes of medication during the previous 4 weeks.
Patients with evidence of acute respiratory failure, i.e. patients with worsening of symptoms
during the previous two weeks, a pH <7.35 or with signs of respiratory infection (two of the
following: coloured sputum, fever, infiltration on the chest x-ray, white blood cell count
>10.000/µL) were excluded. Patients received noninvasive ventilation (NIV) or invasive
ventilation via tracheostomy.
Demographic characteristics, lung function parameters, arterial blood gas values, were
recorded from the last out-patient visit. Each patient completed the SRI and the MOS 36item short-form health survey (SF-36) [1,2]. The underlying diagnoses leading to respiratory
failure were recorded; in cases in which there was more than one condition contributing to
respiratory failure the one deemed to be contributing most was used for categorization
purpose. Patients were categorized into five categories: COPD, restrictive chest wall
disorders (RCWD), neuromuscular disorders (NMD), obesity hypoventilation syndrome (OHS)
and "Miscellaneous".
The Severe Respiratory Insufficiency (SRI) Questionnaire and the MOS 36-item short-form
health survey (SF-36)
The English SRI is the result of transcultural adaptation using forward and back translation
[3,4]. All translators were bilingual professional translators. Their native language was
English, but all of them lived in Germany and were familiar with the conceptual and literal
understanding of the German language. Translators were aware and informed about the
concepts developed in the questionnaire. For forward translation one translator has
translated the questionnaire. In case of difficulties in translating the items the initiator of the
translation process (senior author of the paper) was asked for providing explanations.
Finally, the translator and the initiator of the translation process (native German) met to
agree on a preliminary forward translation. The forward translation was back translated by a
different independent translator. The back translated version was evaluated by the initiator
of the translation process. Items with the same wording compared to original German one
were agreed. Items with a similar sense but slight differences in wording were discussed, but
only changed if a completely congruent wording could have been achieved; otherwise the
translation best fitting was accepted. If an item produced a potentially different sense
comparing the back translated and the original wording, the initiator of the translation
process provided suggestions for rephrasing the items until agreement could be achieved.
This process, however, was not formalised, but eventually, all items could be satisfactorily
translated as care was taken to provide very short and easy to understand items when the
original German version was developed. This was felt necessary as patients eventually filling
in the questionnaire are severely sick and disabled in many ways.
The finally agreed English version was re-evaluated by the initiator of the British study
(second senior of the study) for readability (e.g. clarity, common language use). Revisions
have not become necessary. The final version was used in a pilot in order to see if British
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patients had difficulties in filling in the questionnaire. The final version of the UK English SRI
is provided at the end of this section.
The SRI consists of seven subscales covering 49 items: Respiratory Complaints (SRI-RC),
Physical Functioning (SRI-PF), Attendant Symptoms and Sleep (SRI-AS), Social Relationships
(SRI-SR), Anxiety (SRI-AX), Psychological Well-Being (SRI-WB), and Social Functioning (SRI-SF).
These seven subscales can be summarised to one Summary Scale (SRI-SS). All items relate to
the patients’ circumstances of the last week. Rating for each item is provided by a five-pointLikert-scale, a scaling method which measures either positive or negative responses to a
given statement with five possible grading steps ranging from “strongly agree” to “strongly
disagree”. Scores ranging between 0 and 100 for every scale is possible following
transformation of raw values, as previously described [2]. Higher scores are attributed to
better HRQL.
The SF-36 consists of eight subscales measuring different aspects of health status: SF-36-PF =
Physical Functioning; SF-36-RP = Role-Physical; SF-36-BP = Bodily Pain; SF-36-GH = General
Health; SF-36-VT = Vitality; SF-36-SF = Social Functioning; SF-36-RE = Role-Emotional; SF-36MH = Mental Health. Each subscale produces a standardized score between 0 and 100, with
lower scores indicating poorer health or higher disability [1,5].
Statistical Analysis
Descriptive statistics were calculated by procedure PROC MEANS or PROC FREQ of the
statistical software SAS version 9.1.[6]. Reliability of each sub-scale was calculated as
internal consistency of response among the items assigned to each scale by Cronbach’s
alpha [7]. Values above 0.8 indicate high and above 0.9 very high correlations among the
items of a scale and thus may be interpreted as measuring the same construct. Calculations
were performed with SAS CORR procedure. Normality distribution was tested using the
Kolmogorov-Smirnov test of SAS procedure PROC UNIVARIATE.
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Construct validity was assessed by both explorative factor analysis using principal
components analysis (PCA) and confirmatory factor analysis (CFA). For PCA, only factors with
eigenvalues higher than unity (=1) have been extracted, i.e. the standardized variance of at
least one item variable of the scale is accounted for by the common factor. In addition, the
variance produced by the first and the sum of the first and the second principal component
was reported for each SRI-scale, both for scales which require the extraction of only one
factor (eigenvalue criterion >1), and those scales, which require a two factor solution
(eigenvalues>1 at first and second principal component), respectively. PCA was performed
by SAS PRINCOMP procedure.
CFA was conducted with the software Mplus 4.2 for each of the seven subscales [8]. CFA
allows a formal test of the dimensionality of the construct and is, thus, a rigid procedure to
test the assumed factor structure. Values for standardized factor loadings of an item can
range between -1 and +1 with higher values indicating higher predictive strength of the
latent factor for this item. In other words the items with high factor loadings are good
indicators of the latent construct (common scale). Factor loadings were standardized to both
the latent factor and observed variables' variances of the CFA model. Visual illustration of
the final CFA models for all 7 scales reported in table 6 of main text are listed below (Figures
S1 to S7). The fit for a model with pre-specified common factors was evaluated by the
comparative fit index (CFI) and by the testing that root mean square error of approximation
is less than <0.05 (RMSEA<0.05). CFI -values ≥ 0.95 and RMSEA P-values >0.05 indicate a
good overall fit of the factor model.
Group comparisons on the SRI between patients with different underlying disorders were
performed using analysis of variance (ANOVA) by applying SAS procedure PROC GLM.
Reported P-values were adjusted for multiple comparisons by the methods given by TukeyKramer. A P-value of <0.05 was considered to be statistically significant.
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Figure Legends
Figure S1. Visual illustration of final two factor model of scale Respiratory Complaints
(SRI-RC) reported in table 1 of main text.
Ovals indicate latent factors F1 and F2, which are regressed on the observed variables
(items) indicated by squares (with the respective item number) in the confirmatory factor
model (CFA). The value near the double headed arrow is the correlation between the two
factors F1 and F2. The values near the one-headed arrows are the factor loadings (or
regression coefficients) standardized to both the latent factor and observed variables'
variances of the CFA model.
Figure S2. Visual illustration of final two factor model of scale Physical Functioning (SRI-PF)
reported in table 1 of main text.
Ovals indicate latent factors F1 and F2, which are regressed on the observed variables
(items) indicated by squares (with the respective item number) in the confirmatory factor
model (CFA). The value near the double headed arrow is the correlation between the two
factors F1 and F2. The values near the one-headed arrows are the factor loadings (or
regression coefficients) standardized to both the latent factor and observed variables'
variances of the CFA model.
Figure S3. Visual illustration of final two factor model of scale Attendant Symptoms and
Sleep (SRI-AS) reported in table 1 of main text.
Ovals indicate latent factors F1 and F2, which are regressed on the observed variables
(items) indicated by squares (with the respective item number) in the confirmatory factor
model (CFA). The value near the double headed arrow is the correlation between the two
factors F1 and F2. The values near the one-headed arrows are the factor loadings (or
regression coefficients) standardized to both the latent factor and observed variables'
variances of the CFA model.
5
Figure S4. Visual illustration of final two factor model of scale Social Relationships (SRI-SR)
reported in table 1 of main text.
Ovals indicate latent factors F1 and F2, which are regressed on the observed variables
(items) indicated by squares (with the respective item number) in the confirmatory factor
model (CFA). The value near the double headed arrow is the correlation between the two
factors F1 and F2. The values near the one-headed arrows are the factor loadings (or
regression coefficients) standardized to both the latent factor and observed variables'
variances of the CFA model.
Figure S5. Visual illustration of final two factor model of scale Anxiety (SRI-AX) reported in
table 1 of main text.
Ovals indicate latent factors F1 and F2, which are regressed on the observed variables
(items) indicated by squares (with the respective item number) in the confirmatory factor
model (CFA). The value near the double headed arrow is the correlation between the two
factors F1 and F2. The values near the one-headed arrows are the factor loadings (or
regression coefficients) standardized to both the latent factor and observed variables'
variances of the CFA model.
6
Figure S6. Visual illustration of final two factor model of scale Psychological Well-Being (SRIWB) reported in table 1 of main text.
Ovals indicate latent factors F1 and F2, which are regressed on the observed variables
(items) indicated by squares (with the respective item number) in the confirmatory factor
model (CFA). The value near the double headed arrow is the correlation between the two
factors F1 and F2. The values near the one-headed arrows are the factor loadings (or
regression coefficients) standardized to both the latent factor and observed variables'
variances of the CFA model.
Figure S7. Visual illustration of final one factor model of scale Social Functioning (SRI-SF)
reported in table 1 of main text.
Ovals indicate latent factor F1, which is regressed on the observed variables (items)
indicated by squares (with the respective item number) in the confirmatory factor model
(CFA). The values near the one-headed arrows are the factor loadings (or regression
coefficients) standardized to both the latent factor and observed variables' variances of the
CFA model.
7
REFERENCES
(1) Ware JE, Jr., Sherbourne CD. The MOS 36-item short-form health survey (SF-36). I.
Conceptual framework and item selection. Med Care 1992 Jun;30(6):473-83.
(2) Windisch W, Freidel K, Schucher B, Baumann H, Wiebel M, Matthys H, et al. The
Severe Respiratory Insufficiency (SRI) Questionnaire: a specific measure of healthrelated quality of life in patients receiving home mechanical ventilation. J Clin
Epidemiol 2003 Aug;56(8):752-9.
(3) Higginson IJ, Carr AJ. Measuring quality of life: Using quality of life measures in the
clinical setting. BMJ 2001 May 26;322(7297):1297-300.
(4) Testa MA, Simonson DC. Assesment of quality-of-life outcomes. N Engl J Med 1996
Mar 28;334(13):835-40.
(5) Ware JE, Jr. SF-36 Health Survey. Manual and Interpretation Guide. Boston: The
Health Institute, New England Medical Center Hospitals; 1993.
(6) SAS/STAT 9.1 User's Guide. 2004. SAS Institute Inc,Cary,NC,USA.
Ref Type: Catalog
(7) Nunnally J, Bemstein I. Psychometric Theory. New York: McGraw Hill; 1994.
(8) Mplus Statistical Analysis with Latent Variables, User's Guide [computer program].
Version Version 4. Los Angeles: 2006.
8
Severe Respiratory Insufficiency Questionnaire
SRI
General Health Questionnaire for patients with
Severe Respiratory Insufficiency
Dear patient!
We are treating you for your respiratory disorder. Please fill in this
questionnaire so that we can assess your current state of general health.
Please answer every question by marking the appropriate answer once
with a cross. Participation is, of course, voluntary. All data is bound by
the rules of patient/doctor confidentiality and will be treated in strict
confidence. Your attending physician will be pleased to answer any
questions you may have.
Code number:
9
SRI
The following question relate to your general condition. You will see statements
related to various aspects of daily life.
How did you feel last week? For EVERY statement please mark the answer that
best applies to you.
1. I find it difficult to climb stairs.
completely
untrue
mostly
untrue
sometimes
true
mostly
true
always
true
-2
-1
0
1
2
-2
-1
0
1
2
2.
I suffer from breathing problems
when I eat.
-2
-1
0
1
2
3.
I can go out in the evening.
-2
-1
0
1
2
4.
I often feel miserable.
-2
-1
0
1
2
5.
I suffer from breathing problems
even without physical exertion.
-2
-1
0
1
2
6.
I often have a headache.
-2
-1
0
1
2
7.
I have many friends and
acquaintances.
-2
-1
0
1
2
8.
I worry that my illness might
worsen.
-2
-1
0
1
2
9.
I go to sleep easily.
-2
-1
0
1
2
10. I can deal with other people
easily.
-2
-1
0
1
2
11. I sometimes feel dizzy.
-2
-1
0
1
2
12. I wake up at night with breathing
difficulties.
-2
-1
0
1
2
13. I am afraid of having breathing
difficulties at night.
-2
-1
0
1
2
14. I often have neck pain.
-2
-1
0
1
2
15. I am largely confined to the
house.
-2
-1
0
1
2
16. Housework is difficult for me.
-2
-1
0
1
2
10
SRI
How did you feel last week? For EVERY statement please mark the answer that
best applies to you.
completely
untrue
mostly
untrue
sometimes
true
mostly
true
always
true
-2
-1
0
1
2
17. I often wake up at night.
-2
-1
0
1
2
18. I sleep through the night easily.
-2
-1
0
1
2
19. I am often short of breath.
-2
-1
0
1
2
20. I am optimistic about the future.
-2
-1
0
1
2
21. I feel lonely.
-2
-1
0
1
2
22. I have trouble breathing when I
speak.
-2
-1
0
1
2
23. Visitors exhaust me.
-2
-1
0
1
2
24. I cough a lot.
-2
-1
0
1
2
25. There is often mucus in my
airways.
-2
-1
0
1
2
26. I avoid situations where my
breathing problems might
embarrass me.
-2
-1
0
1
2
27. I feel good when I am with
friends/ acquaintances.
-2
-1
0
1
2
28. I am afraid of having a bout of
difficult breathing.
-2
-1
0
1
2
29. I have difficulties breathing
during physical exertion.
-2
-1
0
1
2
30. I am irritated by the limitations
caused by my illness.
-2
-1
0
1
2
31. My marriage/relationship is
suffering because of my illness.
-2
-1
0
1
2
32. I can go shopping.
-2
-1
0
1
2
33. I can pursue all hobbies that
interest me.
-2
-1
0
1
2
11
SRI
How did you feel last week? For EVERY statement please mark the answer that
best applies to you.
completely
untrue
mostly
untrue
sometimes
true
mostly
true
always
true
-2
-1
0
1
2
34. I am often irritable.
-2
-1
0
1
2
35. My contact with
friends/acquaintances is limited
by my illness.
-2
-1
0
1
2
36. I am enjoying life.
-2
-1
0
1
2
37. I can take part in social events.
-2
-1
0
1
2
38. I am often sad.
-2
-1
0
1
2
39. My breathing difficulties bother
me in public situations.
-2
-1
0
1
2
40. I am often nervous.
-2
-1
0
1
2
41. I can dress myself.
-2
-1
0
1
2
42. I am tired during the day.
-2
-1
0
1
2
43. I feel isolated.
-2
-1
0
1
2
44. I can cope well with my illness.
-2
-1
0
1
2
45. My breathing difficulties impair
me in everyday activities.
-2
-1
0
1
2
46. My family life is suffering
because of my illness.
-2
-1
0
1
2
47. I have broken off contact to
other people because of my
breathing problems.
-2
-1
0
1
2
48. My free-time opportunities are
limited.
-2
-1
0
1
2
49. I am satisfied with life in general.
-2
-1
0
1
2
Thank you!
12
SRI
Severe Respiratory Insufficiency Questionnaire
SRI
General Health Questionnaire for patients with
Severe Respiratory Insufficiency
Guidance for scoring
Please provide the following values for each item:
completely untrue
=>
1
mostly untrue
=>
2
sometimes true
=>
3
mostly true
=>
4
always true
=>
5
The majority of items need to be recoded following the instructions given below:
value
recoded value
Items which need to be recoded:
1
→
5
2
→
4
1, 2, 4, 5, 6, 8, 11, 12, 13, 14, 15,
3
→
3
16, 17, 19, 21, 22, 23, 24, 25, 26,
4
→
2
28, 29, 30, 31, 34, 35, 38, 39, 40,
5
→
1
42, 43, 45, 46, 47, 48.
Next, the scales need to be calculated as indicated below. For this purpose at least
50% of the items per scale must be correctly addressed. Please find the item number
indicated in brackets [a, b, c…..]. This process of transformation produces a score
between 0 and 100 with higher values indicating a better health-related quality of life
according to content of the scale.
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SRI
Respiratory Complaints
Mean[ 2,5,12,19,22,24,25,29] − 1
• 100
4
SRI − RC =
Physical Functioning
SRI − PF =
Mean[1,16,32,33,41,45] − 1
• 100
4
Attendant Symptoms and Sleep
SRI − AS =
Mean[6,9,11,14,17,18,42] − 1
• 100
4
Social Relationships
SRI − SR =
Mean[7,10,21,27,43,46] − 1
• 100
4
Anxiety
SRI − AX =
Mean[8,13,26,28,39] − 1
• 100
4
Psychological Well-Being
SRI − WB =
Mean[ 4,20,30,34,36,38,40,44,49] − 1
• 100
4
Social Functioning
SRI − SF =
Mean[3,15,23,31,35,37,47,48] − 1
• 100
4
Summary Scale
The Summary Scale (SRI-SS) can be calculated by the mean of the values for the
subscales (SRI-RC, SRI-PF, SRI-AS, SRI-SR, SRI-AX, SRI-WB, SRI-SF). The SRISS should not be calculated if one subscale is missing.
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