Psychology Department, Institute of Psychiatry, London
Centre for the Economics of Mental Health, Health Services Research Department, Institute of Psychiatry, London
Psychology Department, Institute of Psychiatry, London
Psychological Medicine, Institute of Psychiatry, London
Correspondence: Dr Dominic H. Lam, Psychology Department, Institute of Psychiatry, DeCrespigny Park, London SE5 8AF. E-mail: D.Lam{at}iop.kcl.ac.uk
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ABSTRACT |
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Aims This 30-month study compares the cost-effectiveness of cognitive therapy with standard care.
Method We randomly allocated 103 individuals with bipolar 1 disorder to standard treatment and cognitive therapy plus standard treatment. Service use and costs were measured at 3-month intervals and cost-effectiveness was assessed using the net-benefit approach.
Results The group receiving cognitive therapy had significantly better clinical outcomes. The extra costs were offset by reduced service use elsewhere. The probability of cognitive therapy being cost-effective was high and robust to different therapy prices.
Conclusions Combination of cognitive therapy and mood stabilisers was superior to mood stabilisers alone in terms of clinical outcome and cost-effectiveness for those with frequent relapses of bipolar disorder.
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INTRODUCTION |
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METHOD |
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Participants
Participants, aged 18-70 years, were out-patients of the Maudsley and
Bethlem NHS Trust with DSM-IV bipolar I disorder
(American Psychiatric Association,
1994). They experienced frequent relapses despite the prescription
of mood stabilisers. Prophylactic medication was prescribed at adequate doses
according to the British National Formulary
(British Medical Association & Royal
Pharmaceutical Society of Great Britain, 2001). Because of relapse
prevention, individuals were currently not fulfilling criteria for a bipolar
episode: Beck Depression Inventory (BDI;
Beck et al, 1961)
score <30, Mania Rating Scale (Bauer
et al, 1991) score <7. This avoided therapists having
to use the majority of therapy sessions to treat an acute episode. In order to
identify a sub-group vulnerable to relapses, participants had to have had at
least two episodes in the previous 2 years or three episodes in the previous 5
years. Exclusion criteria were: actively suicidal (BDI suicide item scored 3)
and currently fulfilling criteria for substance use disorders. There were no
significant differences between the two groups in any of the initial
demographic characteristics or clinical features
(Table 1).
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Assessment and primary clinical outcome
The Structured Clinical Instrument for DSM-IV (SCID;
First et al, 1996) was
used to determine any episode that fulfilled DSM-IV criteria for major
depression, mania or hypomania. The number of days with bipolar episodes was
defined as days during which individuals fulfilled DSM-IV criteria for bipolar
episodes from the SCID interview. Hospital computerised records were used to
confirm the exact length of hospital stays.
Service utilisation
Participants were interviewed using the Client Service Receipt Inventory
(CSRI; Beecham & Knapp,
2001) at baseline and at 3-monthly follow-up visits. The CSRI asks
about specific health and social care service use. Services measured included
contacts with mental healthcare services (psychiatrists, psychologists,
community mental health nurses, day centres, counsellors and other
therapists), general practitioners, social workers, hospital services
(out-patient care, day hospital contacts and accident and emergency
attendances), support groups and residential care.
Details of in-patient stays for mental health and physical health reasons and medication were checked from case notes. Medication use was only recorded every 6 months, and therefore it was assumed that the same level of medication was used in the 3 months prior to this.
Service costs
Unit and hospital costs (which aim to reflect the long-term marginal costs)
for most services were obtained from a recognised national source
(Netten & Curtis, 2000),
where staff costs are calculated by dividing the total cost (salary, oncosts,
overheads, capital, land and training) of the service over 1 year by an
appropriate unit of activity. Medication costs were taken from the British
National Formulary (British Medical
Association & Royal Pharmaceutical Society of Great Britain,
2001). The cost of a cognitive therapy session was assumed to be
equal to 1 h of a psychologist's time (£61). Unit costs were multiplied
by the service utilisation data to generate service costs per patient.
Statistical analyses
Clinical outcome
The main clinical outcome (days with bipolar episodes), which was a
continuous scale, was assessed for group differences using a multivariate
analysis of covariance, covarying the number of previous bipolar episodes and
medication compliance. All analyses were on an intention-to-treat basis. The
primary measure of cost-effectiveness was the number of bipolar-free days
(days without a bipolar episode) in the period following randomisation to
12-month and 30-month follow-up. Bipolar episodes are not a sensitive measure
of relapse prevention, as they can vary tremendously in length.
Resource use data
Comparisons were made between the cognitive therapy and comparison groups
for use of community services (i.e. non-in-patient services combined),
psychiatric in-patient care, general in-patient care and medication. Tests of
significance were only conducted when comparing total costs for each of the
3-month time periods. Hospital use and medication data were available for most
participants. Information on the use of community services was less complete.
Where missing, the cost of community services was imputed by taking the mean
of the costs for the other time periods.
Total cost differences between the groups were tested for statistical significance using a regression model with cost as the dependent variable and the group indicator as the independent variable. Regression analysis allowed us to deal with the expected non-normality of the costs distribution. Non-parametric bootstrapping with 1000 resamples was used to address the skewness in the cost data (Mooney & Duval, 1993). Confidence intervals were constructed at the 90% level because we assumed that it is more acceptable to make a type II error with economic data than with clinical data.
Cost-effectiveness analysis
The incremental cost-effectiveness of cognitive therapy compared with
standard care was determined using the net-benefit approach
(Briggs, 2001). There is
theoretical, but unknown, value (represented by the term below) that
society would place on a 1-unit improvement in outcome, as measured by the
number of bipolar-free days. The net benefit to society of cognitive therapy
can be defined as:
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where NB=net benefit, E=effectiveness (i.e. days free of bipolar episodes
over 12 and 30 months) and SC=service costs. For example, if a bipolar-free
day is assumed to have a value of £10 and if a particular individual has
50 of these, then their gross benefit is £500. However, it is
assumed that is achieved at a cost, and if that is, say, £300 then a net
benefit of £200 is achieved. The trial provided us with data on
effectiveness and service costs. Therefore to estimate a net benefit for each
individual we had to make an assumption regarding the level of .
We estimated net benefits for all participants by assuming different values
for ranging between £0 and £50 in £10 increments. A
regression model was then used to determine the mean difference in net benefit
between the cognitive therapy and standard care (treatment as usual) groups
for every value of
, controlling for baseline costs. For each model,
1000 regression coefficients for the cognitive therapy/standard care variable
were generated using bootstrapping, and the proportion of these greater than
zero indicated the probability that cognitive therapy was cost-effective (i.e.
resulted in a mean incremental net benefit greater than zero) for that value
of
. These probabilities were subsequently used to generate a
cost-effectiveness acceptability curve.
Sensitivity analysis
The only addition to the standard package of care was sessions of cognitive
therapy. The unit cost of this was based on that for a clinical psychologist
from a national source. However, it may be that the actual unit cost could be
different if other professionals (such as mental health nurses) provide the
service, if more or less experienced psychologists deliver the service or if
differences in supervision and general infrastructure affect the costs. To
take into account such possibilities we recalculated the total costs by
assuming that (i) the unit cost of cognitive therapy was 50% lower
(£30.50 per hour) and (ii) 50% higher (£91.50 per hour).
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RESULTS |
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A total of 47% (21/45) in the comparison group v. 38% (18/47) of those receiving cognitive therapy were admitted to hospital for bipolar episodes. The difference was not significant. There was also a non-significant trend for patients receiving cognitive therapy to have fewer days in hospital over the whole 30-month period (mean 31.3 days, s.d.=84.6 v. mean 35.7 days, s.d.=69.8).
Service utilisation
Table 2 summarises service
use for the cognitive therapy and comparison groups in the 3 months prior to
baseline and each follow-up assessment. During the 3 months prior to
randomisation (baseline), 14% (7/51) of the cognitive therapy group received
psychiatric in-patient treatment and 16% (8/52) of the comparison group; 92%
of individuals also received some community services. Virtually all
participants were prescribed medication.
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There were few differences in the proportions of those using these groups of services in the follow-up periods. However, in the 3 months preceding the 6- and 9-month follow-up assessments, around twice as many from the comparison group were admitted compared with those receiving cognitive therapy. However, this was reversed in the period before the 18-month follow-up. Community services continued to be used by the majority of participants throughout the study. Medication also continued to be used by many, but the numbers did decline slightly.
Service cost
Table 3 shows the average
costs at baseline and for each follow-up period. There was much variation in
resource use throughout the study period. Significance tests were only carried
out on the difference between the groups in total costs. For most periods,
there were no statistically significant differences; the exceptions were for
the period up to the 9-month assessment, when the cognitive therapy group was
significantly less costly, and at the 18-month assessment, when the cognitive
therapy group used significantly more resources. These findings were
consistent with the clinical outcomes (Lam et al,
2003,
2005).
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The costs for the 12- and 30-month periods following randomisation are shown in Table 4. For the first 12 months of the study and the whole of the 30 months, the group receiving cognitive therapy had lower service costs. However, the differences were not statistically significant.
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Sensitivity analysis
If the cost of the intervention is reduced by 50%, the total mean cost for
the cognitive therapy group falls to £3952 over the 12-month period
following randomisation but if the cost is increased by 50% the mean rises to
£4815. These changes represent a 10% shift in the average cost. Over the
30-month follow-up period the total cost for the cognitive therapy group falls
to £9925 with the lower unit cost and increases to £10 729 with
the upper bound. This represents a smaller proportional shift (4%).
Figure 2 shows the impact of these new costs on the cost-effectiveness acceptability curves. For clarity only the most extreme results are shown. The best result for cognitive therapy is where the therapy cost is lower by 50% and the outcomes and costs are measured only for the first 12 months. In this situation there is a 93% chance that cognitive therapy is more cost-effective than standard NHS care even if a zero value is placed on a bipolar-free day. The worst case for cognitive therapy is with therapy costs raised by 50% and outcomes and costs measured over the longer period of 30 months. Even here there is a 75.2% chance of cognitive therapy being the more cost-effective option with a zero value placed on a bipolar-free day, and the figure rapidly rises to more than 90% as the value of a bipolar-free day increases.
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DISCUSSION |
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Cost effectiveness
The group receiving cognitive therapy incurred £1000 less service
costs for the first 12 months and £1300 less over the whole 30 months.
However, the difference in total service cost between the cognitive therapy
and comparison group was not significant. As expected, the bulk of the service
cost was for psychiatric in-patient care. Psychiatric in-patient care was very
expensive, leading to highly skewed data. The analysis showed that cognitive
therapy was highly cost-effective compared with standard care alone. Even if
no value is placed on a bipolar-free day, the probability of cognitive therapy
being more cost-effective than standard treatment was more than 80% during the
first year and the whole study period of 30 months. The probability of
cognitive therapy being cost-effective was slightly lower if the whole
30-month period was considered. However, if society is willing to attribute a
value of even £5 to one bipolar-free day, the probability of cognitive
therapy being cost-effective increases to beyond 85% for both time periods.
There are very few cost-effectiveness analyses of interventions for bipolar
disorder; the few there are use outcome measures and methods that differ from
the analyses presented here. Comparisons are not therefore possible. Finally,
the probability of cognitive therapy being more cost effective than standard
psychiatric care is robust in the sensitivity analysis. Even if the cost of
cognitive therapy is increased by 50% (from £863 to £1295), the
probability of cognitive therapy being cost-effective is still high.
Clinical implications
Our results support the addition of cognitive therapy for relapse
prevention in bipolar disorder, particularly for those who are vulnerable to
relapses despite the prescription of mood stabilisers. Clinically, the
combined treatment was significantly more effective. The cost of adding
cognitive therapy to the routine treatment with mood stabilisers and
psychiatric follow-up was offset by fewer costs for other services.
Limitations
There were a number of limitations in this study. First, data on service
use were collected using a self-report questionnaire. Although this allows a
far greater breadth of service use to be measured, it may not be as accurate.
However, the recall period was relatively short (3 months) and data on therapy
and in-patient episodes were collected from other sources. We did not address
the reliability of the service use measures. However, other studies have found
self-report to be an appropriate way of measuring resource use
(Calsyn et al, 1993;
Goldberg et al, 2002). Second, although a broad range of services was included, there were others
that were not measured, such as informal care from family and friends; also
participant time was not costed. Third, we did not have the health economy
data prior to randomisation. However, there was no significant difference
between the two groups in terms of previous hospitalisation, which incurred
most of the health costs. Finally, the study showed that cognitive therapy had
a high probability of being cost-effective but of course it is unknown what
value society places on this. However, the cost-effectiveness acceptability
curves do show the range of values beyond which further increases have a
negligible impact on the probability. Although valuing a bipolar-free day may
have more practical meaning than valuing a point change on a particular
outcome scale, it is still a rather nebulous concept. Further research should
be conducted to determine the views of users, family members and clinicians as
to whether bipolar-free days are meaningful as an outcome measure and, if so,
exactly how they might be valued.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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REFERENCES |
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Received for publication May 18, 2004. Revision received November 9, 2004. Accepted for publication November 17, 2004.