The authors regret that errors were present in the above article. On page 1174, in the second paragraph of the Statistical methods section, the second sentence should read as follows: The incidence of difficult intubation was determined including those whose tracheas were already intubated and is reported as a percentage with a 95% exact binomial CI. On page 1175, in the third paragraph of the Statistical methods section ‘mean standardised difference (MSD)’ should read ‘standardised mean difference (SMD)’ The authors would like to apologise for any inconvenience caused