Clinical Trials

❘❙❚■ Chapter 22 | Intention-to-Treat AnalysisFigure 1. Trial profile for the preeclampsia study described in Example 1 [3].283 women randomized141 assigned to vitamins C and E142 assigned to placebo62 withdrew61 withdrew79 completed the study81 completed the studyWhat is an intention-to-treat analysis?An intention-to-treat (ITT) analysis is a specific strategy for generating the resultsof a randomized controlled trial. Using this method, all subjects are compared inthe treatment groups to which they were originally randomized, regardless ofany treatment that they subsequently received [1,2]. When analyzing the resultsof a study, the ITT method accepts that some subjects might not have compliedfully with their treatment protocol, but assumes that if the subjects arerandomized adequately then noncompliant subjects will be balanced across all thetreatment groups.An alternative method of analysis is to exclude subjects who were not fullycompliant with the study protocol. This form of analysis is known as a perprotocol(PP) analysis, efficacy analysis, or analysis by treatment administered.By focusing only on the fully compliant subjects, one can determine the maximalefficacy of a treatment.Example 1We can illustrate these two methods of analysis (ITT and PP) through thefollowing study on preeclampsia. Preeclampsia is a condition of pregnancy wherewomen have raised blood pressure, fluid retention, and excessive protein in theurine, and may go on to develop seizures. Since an excessive build-up of oxidativechemicals might be responsible, a randomized trial was conducted to see whethersupplementing women at high risk with vitamins C and E (known to haveantioxidant properties) could reduce the frequency of preeclampsia [3]. This study256