Transcript Document

Responsiveness to change and English language validation of the WPAI-GERD questionnaire - results from a Canadian study
Wahlqvist P1, Guyatt G2, Armstrong D2, Austin P2, Barkun A3, Chiba N2, degl'Innocenti A1, El-Dika S4, Fallone C3, Heels-Ansdell D2, Tanser L5, Veldhuyzen van Zanten S6, Wiklund I1, Schünemann H4
1
AstraZeneca R&D Mölndal, Sweden; 2 McMaster University, Hamilton, ON, Canada; 3 McGill University Health Centre, Montreal, QC, Canada;
4
University at Buffalo, Buffalo, NY, USA; 5 AstraZeneca Canada, Mississauga, ON, Canada; 6 Dalhousie University, Halifax, NS, Canada
CONCLUSIONS
Cross-sectional construct validity of the English WPAI-GERD version was confirmed and results indicated that
the WPAI-GERD is responsive to change. Although these results also indicated poor longitudinal construct
validity, the overall findings suggest that further study of the instrument remains warranted.
Change score correlations with QOLRAD dimensions were also according to expectations in general, with a high correlation between productivity
and the “Physical/social functioning” dimension. However, change score correlations between productivity variables and symptom assessments
were low, and these results do not support longitudinal construct validity of the WPAI-GERD.
Table 2. Correlations between productivity variables and other study variables at baseline, at follow-up and change between baseline and follow-up, Pearson
correlation coefficients.
OBJECTIVES
Cross-sectional construct validity of the Work Productivity and Activity Impairment questionnaire for Gastro-Esophageal Reflux Disease (WPAIGERD) has previously been established in a study of Swedish patients consulting a general practitioner because of GERD symptoms.1 The
purpose of this study was to assess cross-sectional and longitudinal construct validity of the English language version, as well as responsiveness
to change of the WPAI-GERD.
METHODS
The WPAI-GERD was used in a clinical study in Canadian GERD patients with moderate or severe symptoms treated with esomeprazole 40 mg
once daily for 4 weeks.2 Productivity variables obtained included GERD-specific hours absence from work, percent of reduced productivity while
at work, and percent of reduced productivity while carrying out regular daily activities other than work during the preceding week. Before starting
treatment, patients completed the Medical Outcomes Short Form 36 (SF-36) questionnaire3 for assessing their health status during the past
week. The SF-36 covers 8 dimensions: Physical Functioning, Role-Physical, Bodily Pain, General Health, Vitality, Social Functioning, RoleEmotional and Mental Health.
Before (at baseline) and after treatment (at follow-up), patients also completed the following questionnaires, all using a one-week recall period:
• Quality of Life in Reflux and Dyspepsia (QOLRAD),4 a GERD-specific health-related quality of life questionnaire with 25 items that combine
into 5 dimensions: Sleep disturbance, Food and drink problems, Emotional distress, Vitality, and Physical/social functioning.
• A questionnaire for assessing severity of four symptoms (Heartburn, Acid reflux, Stomach ache, Belching) using a 7-point Likert scale.
• A questionnaire for assessing severity of overall stomach problems using a 7-point Likert scale.
Cross-sectional validity refers to a validity assessment made at one measured time point, and longitudinal validity refers to a validity assessment
made with regard to a change between two measurements. Evidence of construct validity was in the present study defined as:
• A statistically significant (p<0.05, adjusted for multiplicity) and sufficiently high correlation coefficient (preferably ≥ 0.30 for absence from work
and ≥ 0.40 for other productivity variables) between each productivity variable and other variables where expected.1
Responsiveness to change refers to the extent to which an instrument can accurately measure change in a subject’s condition over time.
Responsiveness was assessed by calculating the effect size (mean change divided by the standard deviation at baseline) for each productivity
variable. An effect size between 0.2-0.5 was defined as small, between 0.5-0.8 as moderate, and >0.8 as large.5
RESULTS
The analysis included 217 patients, of whom 71% (n=153) were employed. Results obtained from the WPAI-GERD during the study period are
shown in Table 1. The improvement (difference from start of treatment) in productivity per patient and week was 0.6 hours for absence from work,
11.0% units for reduced work productivity (=4.7 hours equivalent) and 16.1% units for reduced productivity in daily activities other than work due
to GERD symptoms. This improvement translates into an avoided loss of work productivity of 5.3 hours in total (0.6 + 4.7) on a weekly basis per
patient employed.
Table 1. WPAI-GERD results at baseline, at follow-up and change between baseline and follow-up.
N
Baseline
Mean
Hours absence from work due to GERD
Hours actually worked
Percent reduced productivity, work
Hours lost, reduced productivity, work*
Percent reduced productivity, activities
139
126
130
126
215
0.9
39.7
14.0
5.8
21.0
Follow-up
95% CI
(0.4, 1.3)
(37.5, 42.0)
(11.0, 17.0)
(4.5, 7.1)
(17.9, 24.0)
Mean
0.3
40.0
3.0
1.1
4.9
Change
95% CI
Mean
p-value
(0.1, 0.5)
(37.6, 42.5)
(1.8, 4.2)
(0.6, 1.6)
(3.4, 6.3)
-0.6
0.3
-11.0
-4.7
-16.1
0.011
0.774
<0.001
<0.001
<0.001
* Hours lost due to reduced productivity while at work = number of hours actually worked multiplied by percent of reduced productivity.
Abbreviations: CI = Confidence Interval.
A matrix of baseline, follow-up and change score correlations between productivity variables and other study variables relevant for validation
purposes are shown in Table 2. Cross-sectional correlations (i.e. at baseline or follow-up) were all in the right direction and in accordance with
expectations in general.1 For example, the highest correlation with productivity variables would be expected to be with the QOLRAD dimension
“Physical/social functioning”, which contains specific questions on the impact of GERD symptoms on work and daily activities. Overall, results
support cross-sectional construct validity of the English WPAI-GERD.
SF-36 dimensions:
Physical Functioning
Role-Physical
Bodily Pain
General Health
Vitality
Social Functioning
Role-Emotional
Mental Health
QOLRAD dimensions:
Emotional distress
Sleep disturbance
Food/drink problem
Physical/social functioning
Vitality
Symptom severity:
Stomach pain
Heartburn
Belching
Acid reflux
Overall symptoms
Hours absence from work,
GERD (N=139)
Reduced productivity,
work (N=130)
Hours lost, reduced productivity,
work (N=126)
Reduced productivity,
activities (N=215)
Baseline Follow-up Change
Baseline Follow-up Change
Baseline Follow-up Change
Baseline Follow-up Change
0.12
0.40*
0.27
0.02
0.22
0.38*
0.34*
0.17
-
-
0.41*
0.54*
0.52*
0.31*
0.42*
0.54*
0.43*
0.34*
-
-
0.38*
0.49*
0.49*
0.29
0.36*
0.50*
0.39*
0.32*
-
-
0.49*
0.56*
0.54*
0.40*
0.47*
0.59*
0.52*
0.43*
-
-
0.33*
0.35*
0.33*
0.38*
0.43*
0.15
0.23
0.30*
0.27
0.23
0.27*
0.25
0.22
0.31*
0.30*
0.47*
0.30*
0.36*
0.52*
0.52*
0.62*
0.56*
0.50*
0.62*
0.65*
0.34*
0.18
0.26
0.46*
0.39*
0.43*
0.28
0.33*
0.50*
0.47*
0.57*
0.50*
0.46*
0.55*
0.59*
0.32*
0.17
0.24
0.45*
0.37*
0.49*
0.35*
0.47*
0.63*
0.57*
0.51*
0.46*
0.45*
0.53*
0.54*
0.39*
0.28*
0.34*
0.56*
0.42*
0.19
0.24
0.04
0.18
0.25
0.19
0.24
0.04
0.07
0.16
0.16
0.23
0.06
0.10
0.10
0.30*
0.27
0.18
0.24
0.21
0.43*
0.38*
0.36*
0.50*
0.63*
0.22
0.23
0.10
0.22
0.14
0.25
0.26
0.17
0.21
0.20
0.41*
0.32*
0.36*
0.44*
0.55*
0.14
0.23
0.11
0.18
0.12
0.36*
0.31*
0.18
0.30*
0.34*
0.44*
0.29*
0.31*
0.41*
0.59*
0.20
0.21
0.11
0.23*
0.17
* Statistically significant (=0.05), p-values adjusted for multiplicity (Bonferroni) at each measurement time point: p<0.0007 at baseline, p<0.0013 at follow-up and for change.
Changes in each productivity variable between baseline and follow-up by change in heartburn severity are displayed in Table 3. In patients with a
large or moderate change in symptoms, mean values indicate that a change in productivity is related to the magnitude of change in symptom
severity, which in turn would indicate longitudinal construct validity. However, results also suggest that the insufficiently low change score
correlations found between productivity and symptoms are mainly caused by; (1) high variability in productivity changes between individual
responses, and (2) patients with a small or no change in symptoms also reporting an improvement in productivity.
Table 3. WPAI-GERD results, change between baseline and follow-up by change in heartburn symptom severity.
Improvement in heartburn
symptom severity#
Change in hours absence
from work, GERD
N
Mean (SD)
Change in percent reduced
productivity, work
N
Mean (SD)
Change in hours lost,
reduced productivity, work
N
Mean (SD)
Change in percent reduced
productivity, activities
N
Mean (SD)
+5 or +6
+4
+3
+2
+1 or no improvement
22
24
45
28
20
21
24
41
24
20
21
23
40
24
18
31
43
64
40
37
#
-2.5 (4.5)
-0.5 (3.0)
-0.2 (0.6)
-0.0 (1.9)
-0.2 (2.0)
-18.2 (24.2)
-15.3 (15.7)
-11.0 (14.7)
-3.5 (7.6)
-7.4 (17.3)
-7.2 (9.3)
-7.6 (9.3)
-4.3 (5.6)
-1.6 (3.3)
-3.4 (6.4)
-23.2 (23.5)
-21.0 (20.7)
-15.7 (19.9)
-11.8 (17.6)
-9.8 (19.9)
Number of units improvement between baseline and follow-up in the 7-graded heartburn symptom severity scale. Abbreviations: SD = Standard Deviation.
Results from the effect size calculations are shown in Table 4.
Results indicate moderate responsiveness of each productivity
variable, except for GERD-related absence from work where
the effect size indicates a small responsiveness. Further, the
large and statistically significant changes after treatment
reported in Table 1 are in themselves indicators of responsiveness of all relevant productivity variables.
Table 4. Effect size calculations.
Hours absence from work, GERD
Percent reduced productivity, work
Hours lost, reduced productivity, work
Percent reduced productivity, activities
N
139
130
126
215
Mean
0.22
0.64
0.64
0.71
95% CI
(0.05, 0.38)
(0.47, 0.81)
(0.47, 0.81)
(0.59, 0.84)
Abbreviations: CI = Confidence Interval.
REFERENCES
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2. Schunemann HJ. A randomized multi-center trial to compare utility elicitation techniques with and without hypothetical health states. Quality of Life Research
2003;12(7):A737.
3. Ware JE, Snow KK, Kosinski MA. SF-36 Health Survey Manual and Interpretation Guide. Boston, Massachusetts: New England Medical Centre, 1993.
4. Talley NJ, Fullerton S, Junghard O, Wiklund I. Quality of life in patients with endoscopy-negative heartburn: reliability and sensitivity of disease-specific instruments.
American Journal of Gastroenterology 2001; 96:1998-2004.
5. Cohen J. Statistical power analysis for the behavioral sciences. New York: Academy Press, 1977.