The authors are indebted to the Hamamellis Trust who very generously funded the return travel to London for Dr Nannini to spend a week working on the development of the first review. Thanks to Liz Stovold, Susan Hansen, Karen Blackhall, Jo Picot and Sarah Tracy for technical and clerical support. We are grateful to Karla Soares‐Weiser who extracted data in duplicate for the 2011 update of this review and to Chris Cates for statistical advice and input with calculating SEMs for the included studies for use in GIV analyses.

We would also like to acknowledge the efforts of Inge Vestbo, Diane Grimley and Karen Richardson of GSK who helped us in our attempts to obtain unpublished information on TRISTAN, and of Goran Tornling, Moira Coughlan and Roger Metcalf of AstraZeneca in helping us obtain data for Szafranski 2003. We thank Dr Nick Hanania, Dr Peter Kardos and Prof Donald Mahler for corresponding with us in our attempts to obtain unpublished data from their studies, Dr Dal Negro (Dal Negro 2003) for confirming the SDs in his study and Dr Anzueto for confirming that Ferguson 2008 and Anzueto 2009 are replicate trials.

CRG Funding Acknowledgement: The National Institute for Health Research (NIHR) is the largest single funder of the Cochrane Airways Group.

Disclaimer: The views and opinions expressed therein are those of the authors and do not necessarily reflect those of the NIHR, NHS or the Department of Health.