The changing causal foundations of cancer-related symptom clustering during the final month of palliative care: a longitudinal study

Olson K, Hayduk L, Cree M, Cui Y, Quan H, Hanson J, Lawlor P, Strasser F. The changing causal foundations of cancer-related symptom clustering during the final month of palliative care: a longitudinal study. BMC medical research methodology 2008; 8:36.