What is chronic fatigue syndrome? Heterogeneity within an international multicentre study. by Wilson, A, Hickie, I, Hadzi-Pavlovic, D, Wakefield, D, Parker, G, Straus, SE, Dale, J, McCluskey, D, Hinds, G, Brickman, A, Goldenberg, D, Demitrack, M, Blakely, T, Wessely, S, Sharpe, M, Lloyd, A