Intention-to-treat (ITT) is an analysis of the participants taking part in a clinical trial, based on the group to which they were initially assigned, and not on the treatment eventually received. It does not matter if they drop out, whether they fully adhere to the treatment, or even if they switch to an alternative treatment.

Intention-to-treat analyses are often used to assess the effectiveness of a new treatment because they are seen to reflect real life: not everyone adheres to the treatment they are given, and doctors often change treatments depending on how their patient's condition changes.

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