Comparison of two quality of life instruments for cancer patients: the Ferrans and Powers Quality of Life Index and the European Organisation for the Research and Treatment of Cancer Quality of Life Questionnaire C30.

Health-related quality of life (QoL) in cancer patients cannot be adequately captured with a single instrument. We compared the European Organisation for the Research and Treatment of Cancer Quality of Life Questionnaire (QLQ-C30) and the Ferrans and Powers Quality of Life Index (QLI). We hypothesized that there would be little overlap among their subscales. Baseline QoL data were collected from a consecutive series of 954 cancer patients treated at our center. Data from the two questionnaires were analyzed on a subscale basis using correlation analysis and the Bland-Altman method. The mean and standard deviations of the difference in QoL subscale scores were used to construct 95% limits of agreement among the subscales. Five hundred seventy-nine were females and 375 were males, with a median age of 52 years. There were poor to modest correlations and poor agreement among the subscales of the two instruments. For QLQ-C30 physical and QLI health, the correlation and limits of agreement were 0.6 and -22.2 to 59.8. For QLQ-C30 role and QLI health, the correlation and limits of agreement were 0.6 and -47.3 to 61.5. For QLQ-C30 social and QLI social, the correlation and limits of agreement were 0.2 and -78.2 to 50.2. Consequently, these instruments measure unrelated aspects of QoL and can give different conclusions.