Objective: This study has used Item Response Theory (IRT) to examine the psychometric properties of Health-Related Quality-of-Life.
Method: This investigation is a descriptive- analytic study. Subjects were 370 undergraduate students of nursing and midwifery who were selected from Tabriz University of Medical Sciences. All participants were asked to complete the Farsi version of WHOQOL-BREF. Samejima's graded response model was used for the analyses.
Results: The results revealed that the discrimination parameters for all items in the four scales were low to moderate. The threshold parameters showed adequate representation of the relevant traits from low to the mean trait level. With the exception of 15, 18, 24 and 26 items, all other items showed low item information function values, and thus relatively high reliability from low trait levels to moderate levels.
Conclusions: The results of this study indicate that although there was general support for the psychometric properties of the WHOQOL-BREF from an IRT perspective, this measure can be further improved. IRT analyses provided useful measurement information and demonstrated to be a better methodological approach for enhancing our knowledge of the functionality of WHOQOL-BREF.
Keywords: Item response theory, Psychometrics, Quality of life
Iran J Psychiatry 2010; 5:140-153
In recent years, quality of life instruments have been acknowledged as very important in the evaluation of health care (1). Health-Related Quality of Life (HRQOL) refers to individual's perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards and concerns. It is a broad-ranging concept affected in a complex way by the individual's physical health, psychological state, level of independence, social relationships, and their relationships to salient features of their environment" (2).
There are many general instruments available to measure quality of life. The World Health Organization (WHO) has developed a quality of life instrument, the WHOQOL, which captures many subjective aspects of quality of life) 3-5(. The WHOQOL-BREF is one of the best known instruments that has been developed for cross-cultural comparisons of quality of life and is available in more than 40 languages. It has been adopted in the United State of America, Netherlands, Poland, Bangladesh, Thailand, India, Australia, Japan, Croatia, Zimbabwe and many other countries (6 ,7). During the development of the WHOQOL, it was emphasized that quality of life is a multidimensional
concept (5).According to international standards of WHO, including forward and backward translations, and focus group discussions, Nedjat et al. has translated the WHOQOL into Persian (8). An abbreviated version of the WHOQOL-BREF that contains 26 items is applicable in clinical trials in which brief measures are needed, and also in epidemiological studies in which quality of life might be one of several outcome variables (9). The WHOQOL BREF covers four different domains of quality of life (10). The WHOQOL is under cross-cultural validation by the WHOQOL group (5).
To-date, the studies that have examined the psychometric properties of the WHOQOL-BREF in Iran have all used scores based on the traditional classical test theory (7). Besides the CTT, another approach for examining the psychometric properties of measures is Item Response Theory (10-13).
IRT is a useful tool for gaining insights that traditional techniques cannot provide. Also, it is useful in screening items for inclusion in new questionnaires, and for checking the validity of assumptions even in traditional tests. On the account of these purposes, it certainly deserves wide usage. The most exciting roles for IRT in quality of life(QoL) research, however, lie firstly in the standardization of different instruments so that QoL as assessed by disease- and treatment-specific instruments can be compared across different groups of patients ;and secondly, in the development of computer-administered adaptive testing. …