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Intention to Treat

If we wish to apply the results from a clinical trial to what would happen in general practice, it is generally agreed that all individuals randomized to treatment should be subjected to analysis, irrespective of errors in treatment assignment, breakdown in blinding and withdrawals. This is known as analysis by intention to treat. A trial carried out in this way is said to be a pragmatic trial.

The alternative is to use the exploratory approach where only those complying with treatment are analyzed. In practice the exploratory approach tends to be used in the earlier stages of drug trials on the basis that further research and development may be able to reduce side effects. By the time later trials are underway, a large number of withdrawals suggests a poorly run trial that will be difficult to interpret.

It has been suggested that the definition of intention to treat is somehow unclear:

" ...there is no single definition of an intention to treat analysis, and the phrase seems to have different meanings for different authors."
Hollis & Campbell (1999)

In fact, the definition is very clear. What seems to have happened is that it has become a meaningless phrase that people put in clinical trial reports to get them published - irrespective of how the data have actually been analyzed.