Responsiveness of disease-specific and generic utility instruments in prostate cancer patients

Background: Preferences (utilities) for health outcomes have an important role in decisions about prostate cancer screening and treatment. The responsiveness of utility instruments has not been evaluated. Subjects:: Prostate cancer outpatients from the Princess Margaret Hospital, Toronto (n = 248) were allocated into three cohorts: N - newly diagnosed and treated; M - metastatic disease; O - all others. Measures: We measured quality of life at 3 points within 12 months using 3 disease-specific utility instruments (Patient Oriented Prostate Utility Scales), 3 generic utility instruments (Health Utilities Index, EQ-5D, Quality of Well-Being Scale), and 3 profile scales (PORPUS-P profile, Prostate Cancer Index, QLQ-C-30). Responsiveness was assessed using measures of internal responsiveness (standardized effect size, standardized response mean) and external responsiveness (receiver operator curve analysis, mixed model regression). Results: Cohort N patients showed post-treatment declines followed by improvement in global health and functional status. Disease specific instruments detected moderate (0.4-1.3) decrements followed by small increments (0.1-0.4) in standardized effect size and standardized response mean. Most instruments detected change using external responsiveness measures (all cohorts). Conclusions: Disease-specific utility instruments appeared to be more responsive than generic instruments. Use of generic instruments should be supplemented with a responsive disease-specific instrument, particularly for applications in early prostate cancer.