Lavinia Ferrante di Ruffano1, Jonathan J Deeks2. 1. Department of Public Health, Epidemiology and Biostatistics, University of Birmingham, Edgbaston Campus, Birmingham, B15 2TT, UK. Electronic address: ferrantl@bham.ac.uk. 2. Department of Public Health, Epidemiology and Biostatistics, University of Birmingham, Edgbaston Campus, Birmingham, B15 2TT, UK.