- Correspondence to Almar A L Kok, Department of Epidemiology & Biostatistics, Medical Faculty F-Wing, VU University Medical Center, De Boelelaan 1089a, Amsterdam 1081 HV, The Netherlands;
- Received November 6, 2015
- Revised March 22, 2016
- Accepted April 24, 2016
- First published May 17, 2016.
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