- Correspondence to Inge Stegeman, Department of Clinical Epidemiology, Biostatistics and Bioinformatics (room J1b-210-1), Academic Medical Center, Meibergdreef 9, Amsterdam 1105 AZ, The Netherlands;
- Received January 28, 2013
- Revised August 9, 2013
- Accepted August 20, 2013
- First published September 11, 2013.
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