Quality & Quantity (2007) 41:661–672 © Springer 2006
Identifying Optimal Items in Quality of Life
TING HSIANG LIN
Department of Statistics, National Taipei University, 67, Section 3, Ming-Sheng East Road,
Taipei 10433, Taiwan, ROC. E-mail: email@example.com
Abstract. Quality of life has drawn increasing attention in health science and more efforts
have been devoted to develop instruments that are valid and reliable to assess quality of
life. The World Health Organization (WHO) has devised an instrument World Health Orga-
nization Quality of Life Survey- Abbreviated Version (WHOQOL-BREF) to assess qual-
ity of life, but the psychometric property of each individual item has not been studied yet.
Using item response theory, we examined the properties of the WHOQOL-BRIEF Taiwan
version. Samejima’s graded response model was ﬁtted, and item parameters were calculated.
The items were ranked based on their discrimination power, and the best items were identi-
ﬁed. Several data with subset of items (22, 20, 18, 16 and 14 items) were created by omitting
items with lower discrimination power. The test information function of the full question-
naire and the subsets were compared. The results showed there were signiﬁcant positive cor-
relations between the full questionnaire and the subsets of items and the distributions are
similar. The test information function showed the maximum amount of test information
spaced over two ends of the theta continuum, and this suggested that the WHOQOL-BREF
provided more information for groups with either lower or higher satisfaction of quality of
life, while it is less discriminating for individuals in the middle range.
Key words: WHOQOL-BREF, item response theory, test information.
In the last decade, the concept of “good health” has been recognized as
complete function of physical and mental activities as well as good social
well-being. Quality of life (QOL) has become an important component of
health, and the health care scientists are increasingly concerned about how
to evaluate quality of life. The QOL has been applied in many disciplines
as a method to assess individual’s physical, psychological, social function,
and among others. The World Health Organization (WHO) has developed
World Health Organization Quality of Life Survey (WHOQOL-100) which
consists of 100 items. There are six major domains of WHOQOL-100: envi-
ronment, independence, spirituality, psychological welling, physical capac-
ity, and social relationship. An alternative simpliﬁed four-domain model