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Willingness to Pay for Complete Symptom Relief of Gastroesophageal Reflux Disease
Leah Kleinman, DrPH;
Emma McIntosh, MSc;
Mandy Ryan, PhD;
Jordana Schmier, MA;
Joseph Crawley, MS;
G. Richard Locke III, MD;
Gregory de Lissovoy, PhD
Arch Intern Med. 2002;162:1361-1366.
ABSTRACT
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Background Over $6 billion per year is spent on prescription medication for gastroesophageal
reflux disease (GERD). This study is an economic analysis of patients' willingness
to pay for a prescription medication that offers complete relief of GERD symptoms.
Methods The study was a cross-sectional, nonrandomized design recruiting patients
from 5 clinical sites. A computer-administered discrete-choice questionnaire
was used to explore patients' willingness to pay for various attributes (time
to relief, amount of relief, side effects, and out-of-pocket cost) associated
with GERD treatment. Patients chose between 2 different combinations of attributes
by indicating which scenario they preferred. Data were gathered on health
status, health-related quality of life, and sociodemographic characteristics.
Results Two hundred five patients completed the discrete-choice questionnaire
with a consistency rate of 99.5%. All attributes were relevant to patient
decision making. Respondents were willing to pay up to $182 to obtain complete
relief in a short period of time without side effects. Patients with less
severe GERD symptoms were willing to pay more to avoid side effects ($58.25
vs $38.43). Older patients were less willing to pay for better relief than
younger patients.
Conclusions Results demonstrate that patients are willing to pay more per month
for a medication that provides more complete and faster relief from GERD symptoms.
This information can guide clinicians and formulary committees in evaluating
optimal treatment for GERD.
INTRODUCTION
GASTROESOPHAGEAL reflux disease (GERD) is a common, chronic condition
characterized by the symptom of heartburn. Eighteen percent of the adult population
in the United States reports having had heartburn at least once a week and
almost half of these people have had their symptoms for 10 years or longer.1 Gastroesophageal reflux disease is associated with
substantial use of both prescription and over-the-counter medication and accounts
for several million outpatient visits annually.2
One recent study estimated that over $10 billion is spent annually for the
care of GERD, of which $6 billion is for prescription medication.2
The present study focuses on patient willingness to pay (WTP) for prescription
medication to relieve GERD symptoms. Willingness to pay is defined as an indication
of the monetary value of a commodity or service. Prescription medications
for GERD include H2-receptor antagonists and proton pump inhibitors
(PPIs). Proton pump inhibitors have been shown to be more effective than H2-receptor antagonists3; however, these
medications are costly to patients and insurers. In an effort to control costs,
physicians may choose to manage GERD through an initial trial of H2-receptor
antagonists; if these do not provide symptom relief, patients are switched
to PPIs. Debate continues as to whether this "step up" strategy is preferable
to initial therapy with PPIs.4 Patients may
also use over-the-counter antacids or lower-strength H2-receptor
antagonists either alone or as part of their medication regimen. The presence
of GERD is associated with impaired functioning and quality of life, even
with treatment.5-6
Symptom reduction and complete cure are important goals of medical care
and WTP has been applied to both, depending on the disease or condition in
question. For example, a study of WTP in urinary incontinence7
demonstrated that patients were willing to pay substantially for a 25% to
50% reduction in symptoms ($87.74 and $244.54 per month, respectively). Patients
with psoriasis or atopic eczema were willing to pay between 1253 and 1956
Swedish krona ($151.89-$237.11, 1998 US dollars) for a psoriasis cure and
between 960 and 1083 Swedish krona ($116.37-$131.28, 1998 US dollars) for
an atopic eczema cure.8 Patients with asthma
have been shown to be willing to pay between $200 and $350 more per month
for a cure.9
This study describes an approach to examining attributes of medication
as perceived by GERD patients whose therapy includes prescription drugs and
presents findings. Using an economic methodology known as WTP, the study offers
new insight on the relative importance of specific aspects of treatment.
PARTICIPANTS AND METHODS
The study was a cross-sectional, nonrandomized, experimental design
in which subjects with GERD provided information regarding WTP for complete
relief of GERD symptoms using a computer-administered questionnaire. This
study uses discrete-choice experiments (DCEs) to obtain WTP estimates; other
methods to assess WTP are also available.10-12
Discrete-choice experiments are a type of conjoint analysis. Conjoint analysis
was originally developed for market research and has recently been adopted
by health economists to assess the value to consumers of changes in levels
of health care interventions. In a DCE, individuals are presented with hypothetical
scenarios involving different levels of attributes that have been identified
as important in the provision of a good or service such as a prescription
medication. Attributes are characteristics of the service; in the case of
a medication they might include time to relief, presence and type of side
effects, dosing frequency, and so forth. If one of these product attributes
is a payment vehicle, such as "cost," the DCE can yield marginal WTP estimates
for the other attributes as well as total WTP for combinations of the attribute
levels.13
We explored 4 attributes of treatment relevant to prescription medication
use for GERD, each with 2 to 4 levels. Attributes and levels must be mutually
exclusive, comprehensive, and quantifiable. The attributes used here, determined
through literature review and discussion with expert reviewers, included time
to relief (2, 4, 7, or 14 days until resolution of symptoms), amount of relief
(complete, partial, or none), side effects (presence or absence), and out-of-pocket
cost per month of medication ($5, $15, $35, or $60). The "time to relief"
and "cost" attributes were coded as continuous variables while "amount of
relief" and "side effects" were coded as discrete variables.
The 4 attributes with their levels represented 96 unique scenarios.
Experimental design software (SPEED; Hague Consulting Group, Leiden, the Netherlands)
was used to reduce the number of scenarios to a manageable number while still
permitting inferences about all possible scenarios. Sixteen pairs of scenarios,
that is, pairs of combinations of attributes, were selected to obtain maximum
information from as few paired scenarios as possible. Scenarios were both
exhaustive (so as to explore the full range of attribute levels) and parsimonious
(such that respondents were presented with a relatively small number of scenarios).
Patients selected the scenario they preferred from each pair presented. An
example of a discrete-choice question is provided in Figure 1. Three of the 16 discrete-choice scenarios were tests of
consistency. These scenarios presented choices where one scenario is superior
on all attributes than the other. Respondents would be expected to choose
the better scenario. The interpretation of these consistency checks allowed
for random error; a participant could have failed 1 consistency check without
his or her data being excluded, while patients failing 2 or more were excluded
from the analysis.
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Figure 1. Example of a discrete-choice questionnaire.
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The remainder of the questionnaire gathered information on health status,
disease-specific quality of life, and sociodemographic characteristics.
STUDY SAMPLE
Patients were recruited from 5 clinical sites across the United States.
Sites included gastroenterology clinics within larger health care systems,
a stand-alone gastroenterology clinic, and a research-oriented gastroenterology
facility.
Study participants were 18 years or older, diagnosed as having GERD
for a minimum of 6 months, and under active treatment with prescription medication
for GERD. Patients with concomitant gastrointestinal disorders were excluded.
No random selection or randomization of participants was performed in this
study. Sites were asked to identify and recruit up to 50 study patients.
STUDY SITES AND DATA COLLECTION PROCEDURES
Institutional review board approval was obtained at each site. After
obtaining informed consent, study participants were interviewed at the clinic
site prior to any scheduled medical encounter or procedure. Questionnaires
were administered using a touch-screen–equipped computer system (Assist
Technologies, Scottsdale, Ariz) that has been used successfully in previous
studies of patients with GERD and has proven easy for patients of any age
to use.14-15 The study coordinator
instructed each patient on its use at the beginning of the session. Each of
the 16 DCE pairs (Figure 1) was
displayed sequentially (ie, 1 pair displayed per screen). When a response
was entered, the next item automatically appeared. Patient records were stored
on the hard drive and transmitted by modem to a central location for review
and aggregation across sites. The entire study appointment, including obtaining
consent and completing the questionnaires, took approximately 45 minutes.
OTHER STUDY MEASURES
Disease severity was measured using the heartburn subscale of the Gastrointestinal
Severity Rating Scale.14
The SF-12, a generic health status measure,15
and the disease-specific questionnaire Quality of Life in Reflux and Dyspepsia,16-18 were included in
the questionnaire to help characterize the study population. Questions were
also asked about age, marital status, employment, income level, ethnicity,
sex, educational level, health insurance, and prescription benefit coverage.
All questionnaires were scored according to developer instructions.
ANALYSES
The theoretical framework of the analysis is based on an equation describing
the relationship between the attributes and utility. The simplest specification
of the utility function, the linear additive model,19
assumes that each attribute has an independent and linear effect on consumer
preference. Thus, the marginal effects for each attribute (the amount of extra
satisfaction a consumer gets from obtaining an additional unit of an attribute)
were calculated using a linear additive model. Results were then used to estimate
(1) marginal rate of substitution between the marginal effects of the attributes
(the amount of one attribute an individual is willing to give up to obtain
an additional unit of another attribute while maintaining equal satisfaction),
(2) WTP for changes in levels of specific attributes by estimating the marginal
rate of substitution between the marginal effects on the attributes and the
marginal effect on the "cost" attribute, and (3) overall WTP for a drug with
specified levels of the attributes.
Analysis of DCE data was performed with a random effects probit model
using commercially available software (LIMPED; Econometric Software Inc, Bellport,
NY). A probit model is a form of regression analysis used to estimate a binary
response (ie, the probability of an individual choosing scenario A over scenario
B).
Two models were estimated: a basic model and a segmented model. The
basic model explores mean preferences across the entire group while the segmented
model explores how preferences vary according to predefined subgroups, such
as disease severity. Segmenting the model by income permits the testing of
theoretical validity, whereby it was hypothesized that as income increases,
people are willing to pay more for improvements in symptoms based on an assumption
of more discretionary income being available.
The model was also analyzed by site to assess site-specific variation.
The Wald test19 was used to assess whether
these segmented coefficients are statistically different from each other within
groups. It was expected that increased symptom severity would result in increased
marginal WTP for time to relief, amount of relief, and absence of side effects.20-21 Wald tests were used to test for
significant differences between marginal effects and further z tests22 were used to test for significant
differences in the resulting WTP values obtained by taking the ratio of these
marginal effects with cost. According to a priori theory, it would be expected
that WTP values for reductions in amount of relief would increase with increasing
severity of symptoms.
RESULTS
Two hundred five patients completed the DCE, comprising 3280 individual
observations. There were 33 missing dependent variables that were removed
for analysis purposes, leaving 3247 observations. Results of the consistency
checks showed that only 6 observations from within 5 individuals' responses
were inconsistent. This figure represents an extremely high consistency rate
(99.5%). All observations from the participant who failed this consistency
check were removed for analysis purposes, resulting in 3231 observations from
204 participants.
Over 60% of the patients were women with an average age of 50 years.
More than half the sample had moderate GERD (score of >1 and <4 on the
Gastrointestinal Severity Rating Scale, heartburn subscale). Demographic and
socioeconomic characteristics of the study participants are summarized in Table 1. In general, Quality of Life in
Redux and Dyspepsia subscale scores were high (range, 5.1-6.2), indicating
that patients believed their health-related quality of life was good. The
SF-12 scores were similar to other populations with chronic mild conditions
(physical component summary, 47.7 ± 9.6; mental component summary,
50.1 ± 10.2).15
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Table 1. Demographic and Socioeconomic Characteristics of the 205 Study
Patients*
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Results from the DCE analysis are shown in Table 2. All the marginal effects were significant and had the expected
sign (+ or –), validating the theoretical construct of the model. The
negative sign on "time to relief" indicated that respondents preferred a reduction
in the amount of time required to obtain relief from their GERD symptoms.
The cost coefficient had the expected negative sign demonstrating that the
more expensive the medication, the less likely a person is to prefer it. The
positive sign on amount of relief indicated that the greater the amount of
relief provided by the medication, the more likely a person is to prefer it.
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Table 2. Results From the Basic Probit Model
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Using the marginal effects from Table
2, the marginal rates of substitution between the 4 drug attributes
are estimated and the WTP for changes in levels of these attributes are obtained.
The basic probit model demonstrated that respondents were willing to pay (1)
$2.50 per month for a 1 day reduction in time to onset of relief, (2) $35
per month for an increase in amount of symptom relief from little to some,
(3) $110 per month for an increase in amount of symptom relief from little
to complete, and (4) $41.66 per month for a change in side effects from presence
of side effects to absence of side effects.
Thus, the marginal WTP for a drug that produces no side effects improves
amount of relief from little to complete and reduces the time to relief of
symptoms from 2 weeks to 2 days is $181.66 ([$2.50 x 12] + $110 + $41.66).
Table 3 shows the results
of the segmented random effects probit model assessing the role of symptom
severity on WTP values. The Wald test and the z test
confirm, however, that the marginal effect and resulting WTP values for people
who have moderate disease are greater than those with severe disease for an
improvement in symptoms of "little to some" relief. As expected, however,
the z test shows that people with mild disease are
willing to pay significantly less for improvements in amount of relief (from
little to some) than people with moderate disease. As expected a priori, the
Wald test confirms that people with moderate disease value improvements in
symptom relief (from little to complete) significantly more than people with
mild disease, although the z test does not confirm
this difference to be significant when extracting the WTP estimate from the
ratio of the marginal effects. Finally, and against a priori hypotheses, the
results show that people with severe disease value improvements in amount
of symptoms from little to complete less than people with moderate disease,
although again the z test does not confirm this difference
to be significant when extracting the WTP estimate from the ratio of the marginal
effects (Figure 2).
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Table 3. Willingness to Pay for Amount of Symptom Relief: Comparison
of Subgroups Segmented by Severity of Illness
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Figure 2. Symptom severity and willingness
to pay. Reduction in side effects is from some to none; improved relief is
from little to complete; and faster onset is by 1 day.
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Based on these results, further analysis explored a possible "income"
effect, in which respondents with higher incomes would be willing to pay more
than those with lower incomes. Subgroups were created to test for both income
and severity of illness simultaneously in a bid to control for the possible
effect of income on the WTP values. Each disease severity group was also characterized
by income category. Findings indicated that people with mild disease and a
higher income were willing to pay significantly more to move from little to
some relief than people with mild disease and a lower income ($64.85 vs $32.19)—this
is what we would expect theoretically. However, people within any single income
level (low or high) with mild disease were willing to pay significantly more
to move from little to some relief than those with either moderate or severe
disease ($124.91, $108.25, and $108.86, respectively). Such a result is not
what we would expect theoretically and cannot be explained by an income effect.
Finally, we also examined the effect of demographic characteristics;
no sex effects were demonstrated, but age effects were found. As age increases,
WTP was greater for reduction in time to onset of relief. People older than
60 years were willing to pay significantly less for a unit change in amount
of relief than those in the youngest age group (<46 years). Finally, the
oldest participants were willing to pay more to avoid side effects.
COMMENT
Gastroesophageal reflux disease and GERD-like symptoms affect a large
proportion of the US population.6 This relatively
common condition has a detrimental effect on health-related quality of life
and other measures of functioning. Billions of dollars are spent annually
for over-the-counter medications for GERD. This study demonstrates that patients
are willing to pay fairly large amounts above their insurance prescription
copayments to find effective symptom relief. Results further demonstrate that
DCE is a feasible approach to collecting WTP information in this population.
The basic model showed that overall, patients were willing to pay nearly
$200 additional per month to resolve symptoms, decrease time of onset to relief,
and have no side effects. The level of relief was much more important than
either the presence of side effects or the time to relief. Both physicians
and policy personnel (such as formulary committees) can use this information
to make decisions about prescribing more recent and more expensive medications
for GERD (if these medications can provide the type of relief described in
this study). Physicians can use this information to guide the most appropriate
choice of therapy for an individual patient. Managed care organizations and
insurance companies can use these data to determine copayment for PPIs.
Discrete-choice experiments have been applied successfully in establishing
preferences in several areas of health care decision making.23-31
Further, DCEs have been used to evaluate costs and benefits directly in respiratory
and cardiovascular conditions32 and osteoarthritis.33 The present study not only adds to the literature
on WTP for GERD medications but also used a novel data acquisition method
to do so. Commonly, data for DCEs are obtained via the use of self-completed
mail questionnaires. This study used computer administration as a simple method
of presenting competing scenarios to the patient. The high level of consistency
found in scenario selection indicates that patients had no difficulty using
the computer.
Many of the relationships explored here in segmented models were hypothesized
based on intuition rather than published literature. One would expect that
the relationship between disease severity and WTP is linear, suggesting that
as disease severity increases, people have higher WTP values for relief of
symptoms. However, our results contradict this. Our results suggest that patients
who have mild symptoms might not find them troublesome enough to incur additional
cost whereas patients with severe symptoms while taking medication might be
influenced by this less successful treatment result and in turn have rescaled
their WTP values for symptom relief downwards. This latter "recalibration"
phenomenon is referred to as "response shift."34-36
Schwartz and Sprangers34 define response shift
as a change in the meaning of one's self-evaluation of a target construct;
this may explain our finding that WTP values were not linearly related to
disease severity. Because little is known about this relationship, we offer
these analyses as exploratory and encourage further research. Research in
other areas suggests that the presence and severity of symptoms as well as
whether patients attribute their symptoms to aging or to the disease may affect
their interpretation of the symptoms.20-21
Only 1 other study has assessed WTP in GERD; however, it did not evaluate
WTP for relief of symptoms. The WTP of patients vs proxy decision makers,
namely, physicians and payers, for diagnostic certainty in GERD was assessed
by Hirth and colleagues.37 As expected, patients
were more likely than the other decision makers to value diagnostic certainty.
Willingness to pay values derived from a DCE are more flexible than
those used exclusively in a cost-benefit analysis because marginal WTP estimates
are obtained for each of the individual attributes; hence, this approach facilitates
the estimation of total WTP values for any possible combination of the attribute
levels. Thus, a WTP value for a new drug, not yet on the market, can be estimated
and combined with the projected costs in a bid to determine its worth.
One limitation of the study concerns the sample size. Although the target
sample size included 50 patients from each site, 2 sites did not reach their
enrollment goal, and, consequently, all sites did not contribute equally.
We found no differences between sites, suggesting this limitation is minor.
The sites as well as the patients participating in the study were a convenience
sample; participants were established patients at gastroenterology clinics
who responded to an invitation to participate. Because these persons were
self-selected, they may not be generally representative of GERD patients.
However, the sample was well balanced across disease severity.
Willingness to pay exercises involve hypothetical expenditures rather
than a respondent's actual purchasing decisions. The magnitude of the monetary
values that respondents accorded some attributes appeared rather large, such
as $110 per month for complete relief of symptoms. Results indicate that respondents
valued the "perfect" drug, one with the optimal level of each attribute, at
$182 per month. It is not clear that consumers would commit to payments this
great over the long term. However, other WTP studies have reported similar
findings.
The information resulting from this research can be used as a guide
by clinicians while they interact with the patients to determine an optimal
treatment approach for GERD. By questioning patients on their preferences,
and with knowledge of the patients' prescription benefit plan, clinicians
can be in a position to provide a treatment with the highest patient desirability.
Many managed care plans are instituting multitier copay systems in which the
patient must assume a greater personal financial burden to have access to
the most current, and sometimes more effective, branded medications. The clinician
will need to be skilled in understanding these differences and listening to
how willing a patient may be to pay this additional cost.
Money is the most simple and unambiguous way for individuals to express
the strength of their preferences for treatment characteristics. While 2 patients
may disagree on what the terms "a little" or "somewhat" mean, they are highly
likely to understand the difference between $10 and $20. While these study
results indicate that statistically significant differences were observed
in marginal effects, the real significance of the findings and the message
for the clinicians is the substantial value that patients placed on achieving
complete relief of GERD symptoms, even a willingness to trade-off time to
relief, side effects, and increased out-of-pocket costs. We encourage clinicians
to be aware of this as they are making treatment decisions.
AUTHOR INFORMATION
Accepted for publication October 23, 2001.
Funding for this study was provided by AstraZeneca LP.
Corresponding author and reprints: Leah Kleinman, DrPH, 2601 Fourth
Ave, Suite 200, Seattle, WA 98121 (e-mail: kleinman{at}medtap.com).
From MEDTAP International, Bethesda, Md (Drs Kleinman and de Lissovoy
and Ms Schmier); the Health Economics Research Center, University of Oxford,
Oxford, England (Ms McIntosh); the Health Economics Research Unit, University
of Aberdeen, Aberdeen, Scotland (Dr Ryan); AstraZeneca LP, Wayne, Pa (Mr Crawley);
and the Mayo Clinic, Rochester, Minn (Dr Locke).
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