This is an archived version of the Handbook. For the current version, please go to or search for this chapter here.


We are grateful to members of the Handbook Editorial Advisory Panel: Jane Cracknell, Toby Lasserson, Philippa Middleton, Jonathan Sterne and Lesley Stewart. We are similarly grateful to all members of the previous Handbook Advisory Group for discussions and feedback, and in this role would particularly like to thank Doug Altman, Chris Cates, Mike Clarke, Jon Deeks, Donna Gillies, Andrew Herxheimer, Harriet MacLehose, Philippa Middleton, Ruth Mitchell, David Moher, Donald Patrick, Ian Shemilt, Lesley Stewart, Jessica Thomas, Jane Tierney and Danielle Wheeler.


Many contributed constructive and timely peer review. We thank Phil Alderson, Claire Allen, Judith Anzures, Chris Cates, Jonathan Craig, Miranda Cumpston, Chris Del Mar, Kay Dickersin, Christian Gluud, Peter Gøtzsche, Frans Helmerhorst, Jini Hetherington, Sophie Hill, Sally Hopewell, Steve McDonald, David Moher, Ann Møller, Duncan Mortimer, Karen New, Denise O’Connor, Jordi Pardo, Rob Scholten, Simon Thompson, Jan Vandenbroucke, Janet Wale, Phil Wiffen, Hywel Williams, Paula Williamson, Jim Wright and Diana Wyatt.


Specific administrative support for version 5.0 of the Handbook was provided by Jane Lane. In addition, skilled and generous administrative and technical support provided by Claire Allen, Dave Booker, Jini Hetherington, Monica Kjeldstrøm, Cindy Manukonga, Fiona Matthews, Rasmus Moustgaard, Jane Predl, Jacob Riis and Verena Roloff has contributed greatly to the preparation and co-ordination of this Handbook. We would like to thank Mary Banks, Lucy Sayer, Fiona Woods, Laura Mellor and Jon Peacock at Wiley-Blackwell for their patience, support and advice, and also Neil Manley for providing an index and Wendy Langford for proof-reading.


Version 5 of the Handbook would not have been possible without the generous support provided to the editors by colleagues at the MRC Biostatistics Unit and the Institute of Public Health in Cambridge, UK and at the Australasian Cochrane Centre, Monash University, Australia.