Missing data intention-to-treat

Intention to Treat, Missing Data and Related Matters... 

Chapter 11 Intention to treat, missing data and related matters (Molenberghs and Kenward, 2007)... 

The discussion in the previous section regarding the practical application of the principle of intention-to-treat does not, however, give the full picture. While this principle plus consideration of the per-protocol set may clearly define the sets of subjects to be analysed, we still have to decide how to deal with the missing data caused by failure to complete the study entirely in line with the protocol. 

What impact are the dropouts and missing data likely to have on the definition of analysis sets and in particular our ability to align with the principle of intention to treat ... 

Although the issues of missing data and intention to treat are closely related, they are not identical. Intention to treat analysis is possible provided outcome and randomization data are not missing and (in its strict sense) impossible if they are. If data are not missing, then even if patients are noncompliant it is possible to analyse them as randomized provided only that their original treatment allocation is known. A per-protocol analysis requires knowledge of compliance. Also, depending on what one means by per protocol, it may or may not require complete outcome data. For example, one could simply say for a per-protocol analysis that one is only interested in patients who not only took the medicine as instructed but also recorded their outcomes. 

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