Abstract
BackgroundThe European Organisation of Research and Treatment of Cancer (EORTC) Quality of Life Group is developing computerized adaptive testing (CAT) versions of all EORTC Quality of Life Questionnaire (QLQ-C30) scales with the aim to enhance measurement precision. Here we present the results on the field-testing and psychometric evaluation of the item bank for cognitive functioning (CF).MethodsIn previous phases (I–III), 44 candidate items were developed measuring CF in cancer patients. In phase IV, these items were psychometrically evaluated in a large sample of international cancer patients. This evaluation included an assessment of dimensionality, fit to the item response theory (IRT) model, differential item functioning (DIF), and measurement properties.ResultsA total of 1030 cancer patients completed the 44 candidate items on CF. Of these, 34 items could be included in a unidimensional IRT model, showing an acceptable fit. Although several items showed DIF, these had a negligible impact on CF estimation. Measurement precision of the item bank was much higher than the two original QLQ-C30 CF items alone, across the whole continuum. Moreover, CAT measurement may on average reduce study sample sizes with about 35–40% compared to the original QLQ-C30 CF scale, without loss of power.ConclusionA CF item bank for CAT measurement consisting of 34 items was established, applicable to various cancer patients across countries. This CAT measurement system will facilitate precise and efficient assessment of HRQOL of cancer patients, without loss of comparability of results.
Highlights
One of the most frequently used tools to measure healthrelated quality of life (HRQoL) in cancer patients is the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ-C30) [1]
Since standard item response theory (IRT) models require that items are locally independent, we evaluated the residual correlations from the final factor model
Known group variables that were significant for at least one of the outcomes (QLQ-C30 cognitive functioning (CF) score or one of the computerized adaptive testing (CAT)-based scores) were used to calculate Relative validity (RV). In addition to these evaluations based on the observed data, we evaluated the RV of the CATs based on simulated data across different groups and group sizes [9]
Summary
One of the most frequently used tools to measure healthrelated quality of life (HRQoL) in cancer patients is the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ-C30) [1]. The advantage of CAT is that fewer items are needed to obtain precise measurement and that scores across patients are directly comparable, even if patients do not answer the same subset of items This is enabled with item response theory (IRT) methods [5]. Research and Treatment of Cancer (EORTC) Quality of Life Group is developing computerized adaptive testing (CAT) versions of all EORTC Quality of Life Questionnaire (QLQ-C30) scales with the aim to enhance measurement precision. Conclusion A CF item bank for CAT measurement consisting of 34 items was established, applicable to various cancer patients across countries This CAT measurement system will facilitate precise and efficient assessment of HRQOL of cancer patients, without loss of comparability of results
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