6
Specific Instruments
PROs may also be specific to an area of primary interest [ 15 ]. These instruments are
more limited in scope but are supposed to have favorable measurement properties
and content validity due to their focus on clinically significant aspects of
HRQOL. Because of this, disease-specific PROs are believed to be able to discrimi-
nate more finely between levels of severity of the measured trait, and of being more
sensitive to change. The arthritis impact measurement scales and the gout assess-
ment questionnaire are health profiles that intend to provide information on overall
HRQOL with particular focus on aspects of those respective diseases [ 22 , 23 ].
Measures may also be condition-specific (e.g., depression), or population-specific,
as is the case for many PROs developed for use with juveniles or the elderly.
Domain-specific instruments focus on particular components of health-related qual-
ity of life. Such instruments are typically used when the area covered is of particular
clinical relevance. For instance the Health Assessment Questionnaire Disability
index is a PRO that focuses on physical function alone [ 24 ].
Application of Patient-Reported Outcomes in Different
Settings in Rheumatology
PROs are used in a variety of settings and for different reasons in rheumatology. For
the sake of comparability across studies, researchers and clinicians usually favor the
use of a single patient-reported outcome measure (PROM) in order to facilitate the
comparability across studies. However, because different PRO characteristics and
foci are relevant in different settings, a substantial number of PROs for similar out-
come domains have nonetheless been proposed over time.
Clinical Trials
It is increasingly recognized across all fields of medicine that PROs should be
included as endpoints of clinical trials [ 25 ]. In rheumatology, one of the main rea-
sons for this is that no cure is currently available for most rheumatic diseases and
consequently the primary aim of treatment often is to suppress disease activity in
order to preserve function and structural integrity of the body and/or to manage
symptoms. Many relevant outcomes of rheumatologic care such as pain relief or
effect on mood are known only to the patient. Another motivation for the use of
PROs as (secondary) trial endpoints is that improvements in clinical measures of a
condition may not necessarily correspond to improvements on how the patient func-
tions or feels [ 1 ]. The FDA has stated that “findings measured by a well-defined and
reliable PRO instrument in appropriately designed investigations can be used to
M.A.H.O. Voshaar and M.A.F.J. van de Laar