Randomised clinical trial of manipulative therapy and physiotherapy for persistent back and neck complaints: results of one year follow up. - Koes,B.W.; Bouter,L.M.; Mameren,H van.; Essers,A.H.; Verstegen,G.M.; Hofhuizen,D.M.; Houben,J.P.; Knipschild,P.G. (BMJ, 1992)