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Mortality data
Within a model of disease progression for AD, it is
important to account for mortality over time,
especially as the patient group is elderly and
mortality rates for the elderly with AD are very
high. It is likely that a large number of patients
will die over a period of 5 years. 122 The life
expectancy for patients with AD, from onset of
disease, is thought to be around a mean of 6 years
(SD 3.5 years). 171 The time from onset to
diagnosis and treatment is thought to be between
1 and 4 years.
In the present analysis, a common mortality rate
for all patients is used. Although it is accepted that
there may be differences in mortality by age (as
shown by Burns and colleagues 172 ) and severity,
the data do not allow us to differentiate by these
groups at present. An annual mortality rate of
11.2% is applied in the model (using a monthly
rate in each cycle), using data from Martin and
colleagues, 129 who report a mortality rate of 30%
over 3 years. Sensitivity analysis on the mortality
rate used is undertaken/reported.
Discounting of future costs and benefits
A discount rate of 1.5% has been applied to future
benefits and 6% to future costs. This approach is
the current convention in UK CEA and is in line
with the current guidance from NICE. Other
discount rates have been applied in sensitivity
analysis (0 and 3.5%).
Cost data
Drug costs
Patients in the treatment cohort are assumed to
have been on drug therapy for 6 months prior to
the start of the disease progression model, in
order to accrue effectiveness (improvement on
ADAS-cog) from treatment. Therefore, they begin
the model with an entry cost associated with a
6-month drug cost. Thereafter, the estimated
annual cost for drugs is used (as in Table 56) to
derive a 1-month model cycle cost.
Monitoring costs
Patients in the treatment cohort are assumed to
have been on drug therapy for 6 months prior to
the start of the disease progression model, hence
they begin the modelling process with an entry
cost associated with a 6-month monitoring cost.
Thereafter, the estimated annual cost for
monitoring (see Table 70) is used to derive a
1-month (cycle) cost for monitoring. The
monitoring cost reflects an additional cost, over
and above usual care (covering two additional
outpatient visits), and no allowance is made in our
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Health Technology Assessment 2006; Vol. 10: No. 1
model for the ongoing management costs for the
patient cohort on usual care alone.
Costs for pre-FTC
As discussed above, there is a scarcity of goodquality
information on the costs for AD patients
treated in the community. An estimated cost of
£3937 per year for those patients living in the
health state pre-FTC has been made. This
estimate is based on data from Stewart, 121 and
Kavanagh and colleagues 120 [see the section
‘Costing considerations in the treatment of AD’
(p. 108)], who present overall cost estimates,
reporting that 23% of the overall cost of care falls
on the NHS and PSS budget holder.
Costs for FTC
The cost for FTC has been estimated using the
methods described in Table 71, using data from
numerous sources. Cost estimates for the health
state FTC comprise a proportion of patients in the
health state FTC who are resident in the
community (e.g. own homes) and a proportion
who are resident in an institutional setting. In
estimating the composite cost for FTC, it is
assumed that 48% of those requiring FTC will be
in an institutional setting (base-case analysis). This
estimate is based on data used in studies by Ward
and colleagues 99 and Stewart and colleagues, 82
with further support for this estimate available
from Fenn and Gray, 91 who report a probability of
institutionalisation in severe AD at 45.9%.
Sensitivity analysis on this parameter value is
undertaken (see below).
The estimate for costs related to FTC in a
community setting is £5196 per year, based on
data from the study by Ward and colleagues, 99
where resource use data are from OPCS Surveys 185
(see Appendix 16).
For costs associated with FTC in an institutional
setting, importantly it is believed that not all
institutional costs for AD patients will fall on the
NHS and PSS budget. This has been discussed
above, and an estimate of 30% for the proportion
of patients who are self-funding when in
institutional care (based on findings from Netten
and colleagues 130 ) has been used.
The estimate for FTC used in the SHTAC analysis
comprises (a) institutional care at £18,471 per
year, plus (b) the cost to the NHS and PSS of
caring for these institutionalised patients (over
and above the institutional costs) at £4874 per
year; this estimate is based on resource use data
(for elderly with cognitive disability) from OPCS
123