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Joanne Protheroe a Division of Primary Health Care, Department of
Social Medicine, University of Bristol, Bristol BS8 2PR, b Department of Social Medicine, University of Bristol
Correspondence to: T Fahey
tom.fahey{at}bristol.ac.uk
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Abstract |
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Objective:
To investigate the impact of patients'
preferences for the treatment of atrial fibrillation, by using
individualised decision analysis combining probability and utility
assessments into a decision tree.
Atrial fibrillation is an independent risk factor for
developing stroke. Randomised trials have established that
anticoagulation with warfarin is associated with a relative reduction
in risk of stroke of 68%.1 Community based studies that
estimated the prevalence of atrial fibrillation, however, show
underdiagnosis and undertreatment.
2 3
Commentators
from general practice attribute poor uptake in clinical practice to a
lack of representativeness of patients enrolled in clinical trials. In
particular, patients managed in primary care may find what are deemed
to be "minor" side effects from anticoagulation more
problematic than do highly selected patients in clinical
trials.
4 5
Decision analysis is a form of shared decision making that explicitly
combines the probabilities of events resulting from treatment decisions
with quantitative estimates of the patient's perceptions (utilities)
regarding the consequences of treatment.6 The increasing
computerisation in general practices, along with the development of
user friendly software, means that utility assessment with decision
analysis is a realistic aim for decision making with individual
patients.7
Qualitative research has established that patients' health beliefs are
important factors in determining whether they accept or decline
anticoagulation treatment for atrial fibrillation.8 We
examined the impact of patients' preferences, measured by utility assessment, on treatment choices and compared this method of decision making with evidence based recommendations based on age and comorbidity or absolute risk of stroke.9-11
Selection of participants
Decision analysis
To assess the utility of the health state "treated
with warfarin, experienced side effects, has had cardiovascular
accident, unaffected afterwards" (see fig 1) in a 75 year old
woman The patient is asked to choose between two alternatives: living
in the health state in question until age 80; or living in perfect
health for a shorter length of time. The options are presented on
laminated sheets, and the age to which the patient could live in
perfect health is varied until she is unable to choose between the two
alternatives. Let us suppose that she regards living until age 77 in
perfect health as "equivalent to" living until age 80 in the health
state in question 1 This would be 1
Table 1.
Design:
Observational study based on interviews with patients.
Setting:
Eight general practices in Avon.
Participants:
260 randomly selected patients aged
70-85 years with atrial fibrillation.
Main outcome measures:
Patients' treatment
preferences regarding anticoagulation treatment (warfarin) after
individualised decision analysis; comparison of these preferences with
treatment guidelines on the basis of comorbidity and absolute risk and
compared with current prescription.
Results:
Of 195 eligible patients, 97 participated in
decision making using decision analysis. Among these 97, the decision
analysis indicated that 59 (61%; 95% confidence interval 50% to
71%) would prefer anticoagulation treatment
considerably fewer than
those who would be recommended treatment according to guidelines. There
was marked disagreement between the decision analysis and guideline
recommendations (
=0.25 or less). Of 38 patients whose decision
analysis indicated a preference for anticoagulation, 17 (45%) were
being prescribed warfarin; on the other hand, 28 (47%) of 59 patients
were not being prescribed warfarin although the results of their
decision analysis suggested they wanted to be.
Conclusions:
In the context of shared decision making, individualised decision analysis is valuable in a sizeable proportion of elderly patients with atrial fibrillation. Taking account of patients' preferences would lead to fewer prescriptions for warfarin than under published guideline recommendations. Decision analysis as a
shared decision making tool should be evaluated in a randomised controlled trial.
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Introduction
Top
Abstract
Introduction
Methods
Results
Discussion
References
![]()
Methods
Top
Abstract
Introduction
Methods
Results
Discussion
References
We invited 17 general practices to take part in the study,
of which 13 accepted. Owing to time constraints, only the first eight
practices on an unordered list were included. We identified patients
with atrial fibrillation by means of a diagnostic code on the
practices' computer records and repeat prescriptions for digoxin. We
used random number tables to select patients aged between 70 and 85 years. We sampled 30 or 40 patients per practice, depending on the list
size, yielding a total sample size of 260 patients. In each practice
the list of sampled patients was shown to the general practitioners,
and unsuitable patients were excluded (see the figure on the
BMJ's website). We sent letters and an information sheet
to the remaining patients inviting them to take part in the study. We
then telephoned patients to arrange an interview (with JP) at their
practice; written consent was obtained at the start of the interview.
Details of each participant's risk factor profile were
abstracted from practice records and verified with the participant.
Absolute annual risks of a thromboembolic event were derived from a
literature search and tailored to each individual participant according
to his or her age and comorbidity (table 1). The relative risk
reduction and the probability of side effects if warfarin treatment was
given were also obtained from the literature, as was the likelihood of
functional independence after a stroke (table 1). The treatment
alternatives and their possible consequences were then mapped out by
means of a decision tree (fig 1). The nine health states (outcomes)
from the decision tree were shown on laminated cards to the
participant, who then ranked them in order of preference. Utilities for
each health state were elicited using the "time trade-off" method,
which quantifies the length of time in perfect health that is viewed by
the patient to be equivalent to a given period of ill health
(box). Participants were also asked to complete a short questionnaire
to assess how they felt about the interview
process.
Example of time trade-off method
that is, she would be willing to give up three of
her remaining five years of life to have perfect health. Utility of the
health state in question is then calculated as:
(number of years willing to give up/(80
current age))
(3/5)=0.4, with 0.4 representing the value that this patient places on this state of
health.

View larger version (28K):
[in a new window]
Fig 1.
Decision tree of health states resulting from
having atrial fibrillation with utility values (median (interquartile
range)) for each health state
Data analysis
The probabilities (risks) and utilities were assigned to
each individual's decision tree. These were then multiplied and summed
to give expected utility values for the two main branches of the tree
(treatment and no treatment). After this, a participant was to accept
treatment if the expected utility of "treatment" exceeded that of
"no treatment." In the primary analysis, the probability of
"any" side effects was used; the probabilities for "major" and
"minor" side effects were incorporated into a sensitivity analysis.
this is consistent with
recent guidelines based on absolute risk.11 The result of
the decision analysis was also compared with whether the participant
was receiving anticoagulation treatment at the time of interview.
All these comparisons were performed by using crude percentages of
disagreements between the classifications, both overall and by type of
disagreement. The level of agreement that would be expected by chance
was corrected for using
statistics.15 Ethical approval
was obtained from our local research ethics committee before the start
of the study.
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Results |
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Representativeness
In all, 97 participants completed the decision analysis.
Table 2 shows the characteristics of these participants. The sex ratio
was similar to that for the original sample of 260 patients (55%
female). The participants were also comparable in several respects to
those recruited in the five randomised controlled trials evaluating the
use of warfarin or aspirin in atrial fibrillation, except that women
were underrepresented in the
trials.1
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Proportions recommended for warfarin according to various
criteria
Individuals' utility values varied little within each
health state (fig 1). According to the decision analysis, 59 of the 97 (61%; 95% confidence interval 50% to 71%) participants preferred
treatment with warfarin; the corresponding figures for the other two
recommendations were 89 (92%; 84% to 96%) for the consensus
conference9 and 70 (72%; 62% to 81%) when based on absolute risk.11
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Comparison of decision analysis with recommendations and current
treatment
The primary comparison of the decision analysis based on
"any" side effects with the other recommendations shows a high
level of disagreement (fig 2). Moreover, most of the discrepancies are
"false positives"
for example, of the 38 participants whose decision analysis indicated that they preferred not to be treated with
warfarin, 87% would have been recommended for treatment according to
the consensus conference's guidelines (fig 2). As the chance of minor
side effects is closely similar to that of "any" side effects, the
results of this part of the sensitivity analysis are not shown. Indeed,
even though the risk of major side effects is considerably lower, using
this probability in the calculations for the decision analysis had no
appreciable effect on the results (fig 2). The measure of agreement
(
statistic) for treatment preferences based on decision analysis
and corrected for chance compared with the consensus guidelines and
absolute risk recommendations were 0.09 and 0.25 when "any" side
effects were considered and were 0.05 and
0.04 respectively when
major side effects were considered, indicating "poor" levels of agreement.
that is, contrary to their decision.
Questionnaire responses
Altogether, 82 participants stated a preference to be
involved in shared decision making about their medical care; 67 reported current involvement. Ninety participants thought that the
decision analysis interview could be performed in general practice, by
either their general practitioner or a practice nurse. When asked
whether they found it unsettling to discuss the possibility of having a
stroke or side effects from treatment, 73 said "no," 22 said "a
little," and 2 said that they found it "very" unsettling.
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Discussion |
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Interpretation of findings
When incorporated by means of decision analysis, patients'
preferences could have an important impact on treatment choice in
elderly patients, with nearly 40% of patients with atrial fibrillation
in this study preferring not to receive anticoagulation. Furthermore,
when the results of decision analysis are compared with guidelines
based on absolute risk of stroke, there is marked disagreement (fig 2).
Guidelines ignoring patients' preferences would recommend treatment
for a higher proportion of patients.
at least in the
context of a research study (see figure on the web). This may act as a
barrier to using any form of shared decision making tool in clinical
practice.16 On the other hand, questionnaire responses
from those who participated in decision analysis accord with previous
findings that decision analysis is well accepted by patients, and most
(85%) interviewees would prefer to be involved in clinical decision
making.17
Table 2 shows that apart from an underrepresentation of women, the
participants in this study were not substantially different from
participants in clinical trials for treatment of atrial
fibrillation.1 This suggests that reluctance to apply
results of randomised trials may not be justifiable purely on the basis
of differences in patients' characteristics.4
Comparison with guidelines
Guidelines for anticoagulation in atrial fibrillation based
on absolute risk or clinical criteria have been widely
promulgated.
9 11
Glasziou and Irwig equate one death from
intracranial haemorrhage with prevention of four thromboembolic strokes
and suggest that when the annual risk of stroke exceeds 2% the
benefits start to outweigh the potential harm induced by
anticoagulation treatment.10 This form of absolute
risk assessment has been used as the criterion for judging evidence
based treatment in the community.
9 11
Wide concern has
been expressed that when such criteria are used, atrial fibrillation is
being undertreated in elderly people.
2 3 18
The results
from this study suggest that treatment choice among elderly people is
more complex than simply applying absolute risk standards of treatment.
Factors relating to individual patients have been described and
attributed as one of the reasons for poor uptake of anticoagulation
treatment.19 It seems that among patients who are willing
and able to participate in shared decision making, individual
preferences and probabilities may combine to make some patients more
averse to the consequences of anticoagulation than to the consequences
of atrial fibrillation. The findings of this study suggest that
guidelines for the management of atrial fibrillation should be modified
to incorporate patients' preferences in treatment decisions,
particularly with regard to the consequences of anticoagulation treatment.
20 21
Previous studies
Qualitative research has established the importance of
patients' preferences as a major factor in determining choice of
treatment.8 A randomised trial evaluating the efficacy of anticoagulation treatment shows that quality of life is substantially reduced when patients experience even "minor" side
effects.22 Sensitivity analyses in the current study show
that variation in the severity and likelihood of the side effects for
individual patients has an impact on treatment choice and confirms the
importance of eliciting patients' preferences.23
Study limitations
There are certain constraints with utility assessment,
primarily in achieving a balance between keeping the decision tree as
simple as possible and including all the relevant patient centred
outcomes. It is possible to elicit and then aggregate complex utility
states (such as severity of side effects), but this may be at the
expense of better understanding for the patient and
doctor.27 In this study, therefore, separate utility
values were not elicited for major and minor side effects; rather, all potential side effects were represented together.
Conclusion
In this observational study, eliciting preferences and
performing decision analysis does seem to have important implications for clinical practice. Decision analysis as a shared decision making
tool, and in particular its impact on patients' knowledge, satisfaction, and uptake of and adherence to anticoagulation, should be
examined in a randomised controlled
trial.24
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What is already known on this topic
Qualitative research has established the importance of patients' preferences as a major factor in determining choice of anticoagulation treatment in patients with atrial fibrillation Decision analysis is a form of shared decision making that explicitly combines the probabilities of events resulting from treatment decisions with quantitative estimates of the patients' preferences What this study addsThis study shows that eliciting patients' preferences and performing decision analysis has a major impact on an individual's preference for anticoagulation treatment Evaluation of decision analysis as a shared decision making tool, and its impact on patients' knowledge, satisfaction, uptake, and adherence to anticoagulation treatment, should be examined in a randomised controlled trial |
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Acknowledgments |
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We thank all 13 Avon practices and 260 patients for participating in this study. Both the division of primary health care and the department of social medicine are part of the MRC Health Services Research Collaboration.
Contributors: The study was conceived and designed by TF and TJP. Practices and patients were recruited by JP. Interviews with all the patients were conducted by JP. AAM and JP performed the statistical analyses with input from TF and TJP. TF and JP drafted the paper with contributions from AAM and TJP. JP and TF are the guarantors.
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Footnotes |
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Funding: This study was funded as part of a Wellcome entry level training fellowship for JP. TF receives some funding from an NHS R&D primary care career scientist award.
Competing interests: None declared.
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References |
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Bungard T, Ghali W, Teo K, McAlister F, Tsuyuki R.
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Hlatky M.
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(Accepted 15 March 2000)
Liam Smeeth Epidemiology Unit, London
School of Hygiene and Tropical Medicine, London WC1E 7HT
liam.smeeth{at}lshtm.ac.uk
This paper shows that where good evidence exists decision
analysis is a feasible way of incorporating patients' values and preferences into clinical decisions. The fact that only about half of
the patients who were approached participated should not be viewed
critically: decision analysis will not suit all patients.
Patients' choices of treatment frequently disagreed with both
consensus guidelines and with guidelines based on an assessment of
absolute risk. Overall, the proportion of people who preferred warfarin
treatment was lower than the proportion for whom such treatment is
recommended by either of the guidelines. Patients' preferences did
not, however, all act in the same direction. Considerable numbers of
people preferred warfarin treatment, even though this was not
recommended by either of the guidelines. Given good information, the
participants were able to weigh up the benefits and drawbacks of the
intervention and make a personal choice.
The study shows that when patients are actively involved in clinical
decision making their preferences may strongly influence treatment
decisions. Successfully involving patients in clinical decisions
requires good information. The most reliable source of information
about the effects of interventions comes from sufficiently large, well
conducted randomised controlled trials.1 By definition, however, randomised controlled trials measure the effects of randomly assigned interventions. Randomisation is the key process by which bias
and confounding are minimised. Can the importance of patients' preferences be reconciled with the benefits of randomisation? This
issue has been discussed in depth elsewhere.2-4 The best study design that has been proposed to tackle this dilemma uses a two
stage approach.5 During the first stage, participants are
randomised to two groups: a "random" group and a "preference" group. In the second stage, participants in the random group are randomised a second time to the two interventions being compared in the
trial. Participants in the preference group are given a free choice
between the two interventions being assessed. This design has the
unique advantage of being able to measure the influence of patients'
preferences on the estimate of the treatment effect. Clearly there will
be times when patients' (or clinicians') preferences for one
treatment or another are sufficiently strong to preclude randomisation.
The study by Protheroe et al shows that shared decision making can be
achieved when high quality relevant research evidence about clinical
questions is available to patients and clinicians. Good clinical
practice can then be informed by the evidence; it may not always follow
the evidence.
Competing interests: None declared.
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Footnotes
A figure showing the study profile
appears on the BMJ's website
© BMJ 2000
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