What is meant by intention to treat analysis? Survey of published randomised controlled trials

Objectives To assess the methodological quality of intention to treat analy sis as reported in randomised controlled trials in four large medical journ als. Design Survey of all reports of randomised controlled trials published in 1 997 in the BMJ, Lancet, JAMA, and New England Journal of Medicine. Main outcome measures Methods of dealing with deviations from random alloca tion and missing data. Results 119 (48%) of the reports mentioned intention to treat analysis. Of these, 12 excluded any patients who did not start the allocated interventio n and three did not analyse all randomised subjects as allocated. Five repo rts explicitly stated that there were no deviations from random allocation, The remaining 99 reports: seemed to analyse according to random allocation , but only 34 of these explicitly stated this. 89 (75%) trials had some mis sing data on the primary outcome variable. The methods used to deal with th is were generally inadequate, potentially leading to a biased treatment eff ect 29 (24%) trials had more than 10% of responses missing for the primary outcome, the methods of handling the missing responses were similar in this subset. Conclusions The intention to neat approach is often inadequately described and inadequately applied. Authors should explicitly describe the handling o f deviations from randomised allocation and missing responses and discuss t he potential effect of any missing response. Readers should critically asse ss the validity of reported intention to treat analyses.