Item response theory was used to shorten EORTC QLQ-C30 scales for use in palliative care

Abstract

Background and Objective

The goal was to develop a shortened version of the EORTC QLQ-C30 for use in palliative care. We wanted to keep as few items as possible in each scale while still being able to compare results with studies using the original scales. We examined the possibilities of shortening the physical functioning, cognitive functioning, fatigue, and nausea and vomiting scales.

Study Design and Setting

The shortening was based on 2,366 (physical functioning) and 10,815 (three other scales) observations, respectively. We used item response theory to construct scoring algorithms for predicting scores on the original scales.

Results

Evaluations showed that a three-item physical scale, a two-item fatigue scale, and a one-item nausea or vomiting scale predicted the scores on the original scales with excellent agreement and had measurement abilities similar to the original scales with no loss or only a little loss in power to detect group differences. The results of the cognitive functioning scale indicated problems when predicting scores from a shortened version.

Conclusion

Given the favorable results for the physical functioning, fatigue, and nausea or vomiting scales we expect that the shortened versions of these scales will be included in the abbreviated version of the EORTC QLQ-C30 for palliative care.

Introduction

According to the World Health Organization (WHO) definition, palliative care is the active, total care of patients whose disease is not responsive to curative treatment. The goal of palliative care is to achieve of the best quality of life for patients and their families [1]. Therefore, for descriptive and evaluative studies in palliative care, there is a great need for well-validated questionnaires suitable for measuring the important dimensions of the patient's quality of life. Such questionnaires should be multidimensional, measuring symptom-related aspects as well as psychological, social, and other aspects of the patient's well being. It is crucial that questionnaires are as brief as possible, to keep the response burden at a minimum. Other important considerations when selecting a questionnaire are the measurement (psychometric) properties and the availability of data from published studies for comparisons.

At present, a wide range of questionnaires is used for measuring quality of life in palliative care [2], [3]. This diversity is understandable, because studies may have different research questions and therefore may require different methods. Many questionnaires have similar content, however, and so the diversity may also reflect lack of consensus about the relative merits of different questionnaires. This complicates comparisons of results across studies. Furthermore, many of the available questionnaires used in palliative care have not undergone in-depth psychometric or cross-cultural validation [2].

The European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ-C30) [4], [5] is one of the most widely used disease-specific quality of life questionnaires [6], [7]. The questionnaire is a familiar instrument for many physician researchers and, importantly, published studies and reference data [8] are available for comparisons of results. The QLQ-C30 has been tested extensively for validity, reliability, and other measurement characteristics [4], [9], [10], [11], [12], [13]. These studies have shown the questionnaire to be a generally valid and reliable instrument; however, cancer patients in palliative care are extremely ill and any questionnaire for this field should be as brief and as focused as possible.

We initiated a project to develop a shortened version of the EORTC QLQ-C30 for use with cancer patients in specialized palliative care, that is, patients with advanced, incurable, and symptomatic cancer, who are in contact with hospices, departments of palliative care, palliative teams, or similar support. The methods and results for shortening the emotional functioning scale have been reported; the scale was shortened from four to two items [14]. Another part of this project used interviews with patients (N = 41) and health care professionals (N = 66) from six European countries to determine which domains should be retained in a shortened questionnaire for palliative care. Based on these interviews, it was found that it would be appropriate to develop shortened versions of four additional scales in a palliative care version of the questionnaire: the physical functioning (PF) scale, the fatigue (FA) scale, the nausea or vomiting (NV) scale, and the cognitive functioning (CF) scale. These domains were found to be relevant and suitable for the target group but should optimally be measured with fewer items. That is, in all five of the multi-item scales in the QLQ-C30 should be included in the questionnaire for palliative care in shortened versions if possible.

The aim of the present paper is to evaluate the possibilities for shortening the PF, FA, NV, and CF scales for use in palliative care. We wanted to keep as few items as possible in the scales while still being able to directly compare results obtained with the shortened scales with those from studies using the original, unabbreviated scales. Several approaches have been used to shorten scales including methods based on Cronbach's α, item–scale correlations, factor analysis, and expert opinions (see Coste et al. [15] for a review of methods used to shorten scales). A limitation of all these approaches is that the scores on the shortened scales are not compatible with the scores from the original scales, because they are not on the same metric. We therefore used a new approach, unique in that it seeks to make the scores on the shortened scales compatible with the scores from the original scales. This is accomplished by using item response theory (IRT) [16] to select items for the shortened scales and to construct scoring algorithms for predicting the scores on the full scales from the responses to the items in the shortened scales. This approach to shortening scales was first described in [14] and is further developed, applied, and evaluated in the present paper. That is, the results presented here are also an evaluation of a new approach for shortening scales—an approach that may be used in general to construct shortened questionnaires that are compatible with the original questionnaires.