a randomised controlled trial (MATISSE). - ResearchGate

12 Methods
therapists/facilitators working in a hospital or community setting. Indirect overhead costs
included administrative and managerial support costs and capital overhead costs included the
cost of office space. Total salary and overhead costs were then divided by the average number
of working hours per year, taken from Curtis, 41 to calculate the cost per hour. As well as time in
direct contact with groups, art therapists and activity group facilitators spent time preparing for
the groups and in non-client-related activities, such as training and administration. We therefore
asked each therapist and facilitator to complete a short survey asking how long they spent on
these activities in a typical week. The ratio of direct to indirect client contact that resulted from
this survey was used to calculate the cost per hour of direct client contact. Art therapists and
group facilitators were assisted by co-therapists and facilitators, and their contribution was
calculated by assuming that they were paid as unskilled health-care assistants. In many cases the
assistants were volunteers or students; however, their contribution has been valued monetarily for
the purpose of the economic evaluation as recommended by best practice guidelines 46 and varied
to zero in a sensitivity analysis. The cost per participant was calculated as the sum of therapist/
facilitator and co-therapist/facilitator time in direct client contact for the duration of the groups,
divided by the number per group (eight). We assumed that groups ran for an average of 40 weeks.
Costs were apportioned to each participant on the basis of their randomised status, regardless of
attendance at group therapies. This approach is appropriate here because the groups had closed
entry and because it acknowledges that the resources have effectively been consumed by an
individual at the point of allocation to the group and thus cannot be used by anyone else. 47
Calculation of quality-adjusted life-years
Quality-adjusted life-years (QALYs) were calculated on the basis of the EQ-5D health state
classification instrument, which has five domains: mobility, self-care, usual activities, pain/
discomfort and anxiety/depression. For each domain the respondent chooses one of three
levels of functioning – good to poor. The three levels for each of the five domains are used to
define 243 health states. 48 The health states are then given a utility score using responses from a
representative sample of adults in the UK. 49 The QALYs in the second year were discounted at a
rate of 3.5%, as recommended by NICE. 50 The QALYs were calculated as the area under the curve
as defined by the utility values at BSL and at 12 and 24 months’ follow-up, and it was assumed
that changes in utility score over time followed a linear path. 51 The QALYs were adjusted for
BSL covariates.
Cost-effectiveness analysis
Differences in the use of services between randomised groups at 12 and 24 months’ follow-up
are reported descriptively and are not compared statistically to avoid problems associated
with multiple testing, and because the focus of the economic evaluation was on cost and costeffectiveness.
Costs and cost-effectiveness were compared in two sets of analyses: (1) art therapy
versus standard care and (2) art therapy versus activity groups.
Primary analysis used available case analysis, including those for whom full data at 12 and
24 months were available; there was no imputation of missing service-use observations. Data
on the use of hospital services were available for a larger sample and the impact on results of
using these costs alone were explored in sensitivity analysis. Initially, standard statistical tests
for differences in costs were used. Although costs were not normally distributed, analyses
compared the mean costs between groups using the standard Student’s t-test. Ordinary least
squares regression was used for the adjusted analyses and the validity of results was confirmed
using bootstrapping. 52 This approach, rather than logarithmic transformation or the use of
non-parametric tests, is used in the analysis of cost data because of the need to make inferences
about the arithmetic mean. 53 The primary analysis was of total costs over 24 months. Multiple
regression was used to adjust for the following prespecified BSL characteristics: site, age, sex and