Longitudinal and cross-sectional modelling of health related quality of life in people with cystic fibrosis

Abstract

People with cystic fibrosis (CF) must endure up to four hours treatment per day to maintain health and are vulnerable to complications. The Cystic Fibrosis Quality of Life Questionnaire was developed to measure health related quality of life (HRQoL) in the UK. Most studies on HRQoL are cross-sectional in design with HRQoL measured once per patient. However, the Cystic Fibrosis Quality of Life Questionnaire has been used to monitor HRQoL longitudinally with measures taken over a 12 year period at one clinic in the UK. These data were modelled with a binomial distribution for a domain score and with fixed and random coefficients for the patient-level clinical and demographic variables. The longitudinal study included 182 patients whose HRQoL was first measured within a single calendar year and were then followed-up. These data provided an opportunity to compare, directly and by simulation, the modelling of a cross-sectional with the modelling of a longitudinal study and so provided insights into the statistical merits of longitudinal studies compared to cross-sectional studies in HRQoL.