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1 Centre for Statistics in Medicine, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford OX3 7LD, UK doug.altman@csm.ox.ac.uk.
2 Department of Health Sciences, University of York, York YO10 5DD, UK.
1 Centre for Statistics in Medicine, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford OX3 7LD, UK doug.altman@csm.ox.ac.uk.
2 Department of Health Sciences, University of York, York YO10 5DD, UK.