Two Kinds of Items in Quality of Life Instruments: ‘Indicator and Causal Variables’ in the EORTC QLQ-C30

Abstract

Two kinds of variables may be differentiated within instruments measuring health-related quality of life (HRQOL). Physical symptoms may be called causal variables because their occurrence can cause a change in HRQOL, but poor HRQOL need not necessarily imply that a patient suffers from these symptoms. Other items can be regarded as indicator variables. They reflect the level of HRQOL and a patient with a poor HRQOL is likely to have low scores on all indicator variables. The aim of this study was to test the relationship of the latent HRQOL construct to items and domains on the EORTC QLQ-C30. Confirmatory factor analysis was performed on EORTC QLQ-C30 data from 205 gastrointestinal cancer patients assessed one month after surgery. Functioning scales were established as variables indicating the level of HRQOL whereas all other subscales and items were established as variables causing a change in HRQOL. The model-data fit was satisfactory. Results support the hypothesis that two kinds of variables may be differentiated within HRQOL instruments. Further research should investigate whether both kinds of variables could be combined into a higher order, aggregate score for HRQOL.

Prostate cancer patients’ quality of life assessments across the primary treatment trajectory: ‘True’ change or response shift?

“…This assumption, which is consistent with results from previous studies [13,14], proved tenable. Our results are also in line with studies that found evidence for recalibration response shift in prostate cancer [6][7][8][9].…”

“…Although our choice of a single underlying factor fitted the data well and was proven by previous research [13,14], other models are conceivable [24]. As structural equation modeling rests upon group statistics, our results pertain to the whole sample of patients and we were not able to examine response shift on an individual level.…”

“…Physical, Role, Social, Cognitive, and Emotional functioning, respectively, represent an underlying functioning QoL factor. This assumption has been tested empirically and proved tenable [13,14].…”

Assessing patient-reported peripheral neuropathy: the reliability and validity of the European Organization for Research and Treatment of Cancer QLQ-CIPN20 Questionnaire

“…Consistent with the published descriptions regarding the differences between formative versus reflective measurement models, the QLQ-CIPN20 is most consistent with a reflective measurement model because it is comprised of indicator, not causal, variables [19, 20]. Specifically, changes in observed variables/items such as tingling or burning/shooting pain indicate that CIPN is present.…”

Fatigue after treatment in breast cancer survivors: prevalence, determinants and impact on health-related quality of life

“…Participants were classified as having the symptom if the symptom scale score was 66 or higher. In this case, symptoms were established as causal variables because their occurrence can affect health-related quality of life, as suggested in a previous study [38].…”