1. Ludwig-Maximilians-University Munich; Institute for Medical Informatics, Biometry and Epidemiology; Marchioninistr. 15 Munich Bavaria Germany
2. Health Effects Institute; 101 Federal St Boston MA USA
3. Information Services, Cardiff University; Support Unit for Research Evidence (SURE); 1st Floor, Neuadd Meirionnydd Heath Park Cardiff Wales UK CF14 4YS
4. Stellenbosch University; Centre for Evidence-based Health Care, Faculty of Medicine and Health Sciences; Francie van Zijl Drive Cape Town South Africa 7505