Abbreviated World Health Organization Quality of Life questionnaire (WHOQOL-Bref) in north Indian patients with bronchial asthma: an evaluation using Rasch analysis

Abstract

Background: There is no disease-specific instrument to describe health-related quality of life (HRQoL) in Indian patients with asthma. However, an abbreviated World Health Organization Quality of Life questionnaire (WHOQOL-Bref), a generic Hindi HRQoL measure, has been developed and validated in India.

Aims: To evaluate the WHOQOL-Bref in adult patients with asthma and to test possible modifications to the instrument to improve its psychometric adequacy.

Methods: Sixty-seven patients with asthma completed the WHOQOL-Bref. Rasch analysis was used to explore the psychometric performance of the four domains (physical, psychological, social relationships and environment) of the scale. Overall fit of data to model expectations, appropriate category ordering, presence of differential item functioning, individual item fit and targeting of item difficulty to patient ability were explored for each domain. Item deletion and rescoring were applied to misfitting items to improve overall performance.

Results: The overall fit of the WHOQOL-Bref data was adequate. Item 3 (pain prevents doing work) displayed a large positive fit residual value (indicating violation of unidimensionality), resulting in poor construct validity for the physical domain. No item exhibited differential item functioning. Ten items had disordered thresholds. The WHOQOL-Bref was modified by dropping item 3 and rescoring category structures of 16 items. The modified scale had good construct validity for all domains, ordered thresholds for all items and good targeting of items to persons.

Conclusions: The WHOQOL-Bref performed inadequately in describing HRQoL in the asthma patients studied. However, when modified by Rasch analysis, the scale proved better than the original scale.

Figure 1

Graphical exploration of differential item functioning for item 18 (capacity for work) of the abbreviated World Health Organization Quality of Life. The dashed line corresponds to the item characteristic curve representing the expected probability of item endorsement as a function of person ability. Superimposed plots represent the observed responses by patients of either gender (left panel), different age groups (middle panel) and different levels of asthma control (right panel). For each analysis, patients were divided into three approximately equal groups according to their health-related quality of life. Individual plots for each analysis lie close to each other, with no obvious dissimilarities. Group differences were also statistically non-significant on formal analysis of variance testing, suggesting that item response functions were largely invariant across categories.

Figure 2

Example of category probability curves. The top panel for item 12 (money to meet needs) of the abbreviated World Health Organization Quality of Life reveals disordered and reversed thresholds. There is no point on the continuum where response categories 2 or 4 are the most likely responses. Threshold locations (corresponding to points of intersection between probability curves of two adjacent response categories) between response 1 or 2 and 2 or 3, and between 3 or 4 and 4 or 5, are reversed. The bottom panel shows the curves redrawn after rescoring category structure (collapsing categories 1 and 2, and 4 and 5). After this merger, the three response categories for this item are well ordered and distributed, with persons with higher ability (or better quality of life) having a progressively greater probability of endorsing a higher response category.

Figure 3

Person-item distribution maps for various domains of the abbreviated World Health Organization Quality of Life (WHOQOL-Bref) after rescoring categories. The vertical line represents the measure of the variable in linear logit units. In each panel, the right-hand column locates questionnaire item threshold difficulty measures along the variable. Each entry is indicated by its number in the original questionnaire (see Table 1), followed by the threshold after the decimal point. For instance, the location 04.3 refers to the difficulty calibration estimate of the third threshold (i.e., threshold between the third and fourth response category) of the fourth questionnaire item. The left-hand column locates the patients’ ability measure along the variable, with each plus sign representing 10 patients and each circle representing one patient. From bottom to top, measures indicate better health-related quality of life (for patients) and greater difficulty (for items).