The Functional Living Index-Cancer: estimating its reliability based on clinical trial data

The Functional Living Index-Cancer was developed to measure quality of life in cancer trials as an adjunct to the usual clinical outcomes. The scale is considered conceptually good, since it covers a broad range of relevant aspects of quality of life, but the main criticism has been that its reliability has never been properly investigated. In this paper, we investigate the reliability of the FLIC.We apply a new methodology based on linear mixed models that allows estimating reliability from real clinical data. The reliability of the FLIC is estimated using data coming from a longitudinal study in breast cancer. With this new approach, we avoid the need for additional data collection on which classical reliability studies are based.The average reliability of the FLIC over the repeated measurements is satisfactory, even though the initial measurement in the study showed a somewhat lower value. Taking into account the longitudinal character of the measurements, we show that highly reliable information can be obtained with a relatively small number of measurements per patient.The FLIC provides reliable quality of life measurements in patients with breast cancer. Additional studies would be welcome to validate these results in other populations.