Salvatore Stefania, Bramness Jørgen G, Røislien Jo
Norwegian Centre for Addiction Research, University of Oslo, Oslo, Norway.
Oslo Centre for Biostatistics and Epidemiology, Institute of Basic Medical Sciences, Oslo, Norway.
BMC Med Res Methodol. 2017 Feb 23;17(1):34. doi: 10.1186/s12874-017-0311-y.