Assessing Emotional Functioning with Increased Power: Relative Validity of a Customized EORTC Short Form in the International ACTION Trial
Objectives: There is a need to improve the assessment of emotional functioning (EF). In the international Advance Care Planning: an Innovative Palliative Care Intervention to Improve Quality of Life in Cancer Patients - a Multi-Centre Cluster Randomized Clinical Trial (ACTION) trial involving patients with advanced cancer, EF was assessed by a customized 10-item short form (EF10). The EF10 is based on the European Organisation for Research and Treatment of Cancer (EORTC) EF item bank and has the potential for greater precision than the common EORTC Quality of Life Questionnaire Core 30 four-item scale (EF4). We assessed the relative validity (RV) of EF10 compared with EF4. Methods: Patients from Belgium, Denmark, Italy, the Netherlands, Slovenia, and the United Kingdom completed EF10 and EF4, and provided data on generic quality of life, coping, self-efficacy, and personal characteristics. Based on clinical and sociodemographic variables and questionnaire responses, 53 “known groups” that were expected to differ were formed, for example, females versus males. The EF10 and EF4 were first independently compared within this known group, for example, the EF10 score of females vs the EF10 score of males. When these differences were significant, the RV was calculated for the comparison of the EF10 with the EF4. Results: A total of 1028 patients (57% lung, 43% colorectal cancer) participated. Forty-five of the 53 known-groups comparisons were significantly different and were used for calculating the RV. In 41 of 45 (91%) comparisons, the RV was more than 1, meaning that EF10 had a higher RV than EF4. The mean RV of EF10 compared with that of EF4 was 1.41, indicating superior statistical power of EF10 to detect differences in EF. Conclusions: Compared with EF4, EF10 shows superior power, allowing a 20% to 34% smaller sample size without reducing power, when used as a primary outcome measure.