Background/Purpose: The ASAS Health Index (HI) was developed to assess the impact of
spondyloarthritis (SpA) on the patients’ overall function and health. Utilities
are a special type of health-assessment measures that reflect a ‘preference’
for the different health states that patients with SpA can experience.
Utilities range from 0 (death) to 1 (perfect health). While the patient’s
preference is increasingly recognized as resource for utilities, preferences
from the general population remain the corner stone in healthcare decisions.
Therefore, the aim of this study was to develop a conversion tariff for the
ASAS HI to derive utility of health states of patients with SpA from the
perspective of the general population. As it is known that preferences can be culturally
dependent, we also derived country specific utilities.

Methods:
An online survey was performed in a random sample of subject from the general
population in the UK, France, Germany, the Netherlands, Spain and Italy.
Subject completed first the ASAS HI. Next, two lead Time Trade Off (LTTO)
experiments were performed to anchor the health states defined by the ASAS HI
on a 0 to 1 utility scale. The lowest value was based on the health state
‘severe SpA’ and the highest value on their ‘own ASAS-HI health state’. ‘Severe
SpA’ was defined by impairments in 8 items of the ASAS HI, selected previously
by patients as having  most impact on their health. In addition, subjects
completed a Best-Worst Scaling (BWS) experiment comprising 17 choice tasks to
assess the relative contribution of each item of the ASAS HI to overall health.
Finally, the relative importance score of each item of the ASAS HI as derived
by BWS, was used to rescale the ‘value of health’ between the anchors of worst
and best health defined in the LTTO.

Results:
In total, a representative sample of 3,039 persons from the general population
(age 46.5 years (SD 15.2), 1556 women (52.2%)) contributed to the analysis
(about 500/country). As analyses showed comparable results among countries, we
here present the overall results. Table 1 shows the results of the contribution
of each item in the ASAS HI to the utility conversion formula. It can be seen
that an individual who has no health problems related to SpA would experience a
utility as 0.92. On the other hand, subjects of the general population indicate
that the utility of a patient with SpA that scored problems on all 17 items of
the ASAS HI would be as low as -0.37: a health state worse than death. A patient
with SpA with pain, problems in sleeping, and problems with standing would be
considered by society to have a utility of 0.59. Further analyses showed these
results were largely comparable across countries.

Conclusion:
From now onwards, a European transformation formulae is available to convert
scores on the ASAS HI in a utility of the societal perspective. This makes it
possible to use disease specific utilities in cost-utility analyses in patients
with SpA.