Validity and reliability of the English and translated Chinese versions of the Integrated Palliative care Outcome Scale (IPOS) in Singapore

Abstract

CONTEXT: Measurement of patient-centred outcomes enables clinicians to focus on patient and family priorities and enables quality of palliative care to be assessed. OBJECTIVES: This study aimed to evaluate the validity and reliability of the English and translated Chinese versions of the Integrated Palliative care Outcome Scale (IPOS) among advanced cancer patients in Singapore. METHODS: IPOS was forward and backward translated from English into Chinese. Structural validity was assessed by confirmatory factor analysis; known-group validity by comparing inpatients and community patients; construct validity by correlating IPOS with Edmonton Symptom Assessment System-revised (ESAS-r) and Functional Assessment of Cancer Therapy-General (FACT-G); internal consistency by Cronbach's alpha; inter-rater reliability between patient and staff responses; test-retest reliability of patient responses between two timepoints. RESULTS: One hundred eleven English-responding and 109 Chinese-responding patients participated. The three-factor structure (Physical Symptoms, Emotional Symptoms and Communication and Practical Issues) was confirmed with Comparative Fit Index and Tucker-Lewis-Index > 0.9 and Root Mean Square Error of Approximation < 0.08. Inpatients scored higher than outpatients as hypothesised. Construct validity (Pearson's correlation coefficient, r ≥ |0.608|) was shown between the related subscales of IPOS and FACT-G and ESAS-r. Internal consistency was confirmed for total and subscale scores (Cronbach's alpha≥0.84), except for the Communication and Practical Issues subscale (Cronbach's alpha = 0.29-0.65). Inter-rater reliability (Intra-class correlation coefficient [ICC] ≤ 0.43) between patient and staff responses was insufficient. Test-retest reliability was confirmed with Intra-class correlation coefficient ICC = 0.80 (English) and 0.88 (Chinese) for IPOS Total. CONCLUSION: IPOS in English and Chinese showed good validity, good internal consistency, and good test-retest reliability, except for the Communication and Practical Issues subscale. There was poor inter-rater reliability between patients and staff.