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Bibliography:Correspondence to: Dr Aylin p.aylin@ic.ac.uk
Contributors: JB was responsible for the extraction and interpretation of the data. BDeS conducted the statistical analysis and contributed to interpretation and reporting. MPC contributed to the study design, interpretation, and drafting the report. PA took the initiative in this study and contributed to the study design, analysis, interpretation of the results, and drafting the paper. PA is the guarantor.
ISSN:0959-8138
1756-1833
1468-5833
DOI:10.1136/bmj.318.7190.1044