Methodological issues of patient utility measurement. Experience from 2 clinical trials

This article explores various methodological issues of patient
utility measurement in two randomized controlled clinical
trials involving 85 patients with fibromyalgia and 144 with
ankylosing spondylitis. In both trials one baseline and two
follow-up measurements of the patients' preferences for their
own health state and several hypothetical states were
performed using the rating scale and the standard gamble

It was confirmed that standard gamble scores are
consistently higher than rating scale scores for both the
experienced and the hypothetical states. The 3-month
test-retest reliability for hypothetical states measured by
intraclass correlation coefficients ranged from 0.24 to 0.33
for the rating scale and from 0.43 to 0.70 for the standard
gamble. Although the reproducibility is not high, the group
mean scores are fairly stable over time. Mean standard gamble
scores tend to differ depending on the way the measurements
are undertaken.

Utilities elicited with chained gambles were
significantly higher than utilities elicited with basic
reference gambles. At the individual level some inconsistent
responses occurred. However, more than 70% of these fell
within the bounds of the measurement error, which ranged from
0.11 to 0.13 on the standard gamble (0-1 scale) and from 8 to
10 on the rating scale (0-100 scale). The large number of
negative utilities for the severe hypothetical state, which
was used as an anchor point in the chained gambles, and the
magnitude of these negative utilities (down to -19) calls for
intensified research efforts to handle these responses in
utility calculations.

Rutten-van Molken MP, Bakker CH, van Doorslaer EK, van der Linden S

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