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Sally Hollis a Medical Statistics
Unit, Fylde College, Lancaster University, Lancaster LA1 4YF, b AstraZeneca,
Mereside, Alderley Park, Macclesfield, Cheshire SK10 4TG
Correspondence
to: S Hollis s.hollis{at}lancs.ac.uk
Objectives:
To assess the methodological quality of
intention to treat analysis as reported in randomised controlled trials in four large medical journals.
Design:
Survey of all reports of randomised controlled trials published in 1997 in the BMJ, Lancet, JAMA,
and New England Journal of Medicine.
Main outcome measures:
Methods of dealing with
deviations from random allocation 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 intervention and three did not analyse all randomised
subjects as allocated. Five reports 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 missing data on the
primary outcome variable. The methods used to deal with this were
generally inadequate, potentially leading to a biased treatment effect.
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 treat approach is often
inadequately described and inadequately applied. Authors should
explicitly describe the handling of deviations from randomised
allocation and missing responses and discuss the potential effect of
any missing response. Readers should critically assess the validity of
reported intention to treat analyses.
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