Background: The aim was to compare two individualized patient reported outcomes or the Schedule for the Evaluation of Individual Quality of Life - Direct Weighting (SEIQoL-DW) measuring quality of life in general, and the disease-related version (SEIQoL-DR) measuring quality of life related to disease. Both instruments have been used in clinical practice settings within oncology. The instruments were compared with regard to feasibility, the areas nominated by patients as important and patients' ratings of how they were doing in these areas (Index scores).
Material and methods: The study included 40 patients with gastrointestinal cancer. All patients completed both versions of the instrument on a touch screen computer in relation to a medical consultation. Firstly, the participants were invited to nominate the five domains she/he currently considered to be most important in life. Secondly, they were asked to rate how they were doing in each of these domains. Finally, they were asked to quantify the relative importance of each area. Cohen's effect sizes were calculated to illuminate the clinical importance of mean value differences.
Results: Both instruments took less than ten minutes to complete and the procedure was considered feasible by both patients and interviewers. The proportion of patients nominating the same areas in the two versions did not differ, however, the SEIQoL-DW Index score was significantly higher than the corresponding score for the SEIQoL-DR. The detected difference in the mean score measured by effect size was medium.
Conclusion: The magnitude of the effect size of the difference in Index score imply that the two versions tap into different constructs, i.e. quality of life (QoL) versus health-related QoL (HRQL), supporting the construct validity of the two versions of the instrument. The SEIQoL-DW and the SEIQoL-DR should be considered as complementary rather than interchangeable when used in patients with cancer.