The Elderly Functional Index (ELFI), a patient-reported outcome measure of functional status in patients with cancer: a multicentre, prospective validation study

Functional assessment of patients with cancer can be challenging and is often undertaken by the clinician with minimal direct input from the patient. We developed and aimed to validate the Elderly Functional Index (ELFI), a composite measure of self-reported functioning in older patients with cancer. In this multicentre, prospective validation study, we validated ELFI in adult patients attending five oncology practices in Australia. ELFI is a 12-item composite measure of self-reported functioning derived from functional scales of the European Organisation for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire (QLQ): physical, role, and social functioning, and mobility. For evaluation of validity and internal consistency, participants self-completed ELFI, cognitive functioning and emotional functioning scales of the EORTC QLQ Core-30, Eastern Cooperative Oncology Group Performance Status (ECOG-PS), instrumental activities of daily living (IADL), and Clinical Frailty Scale (CFS) at baseline. For evaluation of test–retest reliability, participants opted in to repeat ELFI, cognitive functioning scale, emotional functioning scale, and ECOG-PS 1 week later, as well as completing the Global Rating of Change. Internal consistency reliability was assessed using Cronbach's α and test–retest reliability was assessed using intraclass correlation (ICC). We assessed ELFI for convergent and discriminant validity (Spearman's r), known-groups validity (ANOVA), and structural validity (exploratory factor analysis). Between May 6 and Dec 15, 2017, 877 participants with cancer returned a total of 869 baseline questionnaires and 482 retest questionnaires. 621 (71%) participants (192 [31%] aged ≥70 years) were included in evaluations of validity and internal consistency and 278 (32%) participants (106 [38%] aged ≥70 years) in evaluations of test–retest reliability. ELFI demonstrated excellent internal consistency reliability (Cronbach's α=0·93 for all participants; p