i think intention to treat should be considered in non-randomly assigned groups. Just thinking about a study of a programme to change behaviour (smoking). Group A nominated themselves for the programme, but 40 out of 50 of them did not complete it, it was sooo boring. It would be unfair to compare the 10 who did complete with the comparison group. The Intention to treat principle is important because drop-outs shew your data, and if your intervention/drug is to be assessed comprehensively surely you need findings that account for the likelihood that people don't finish the intervention/drug prescription.

I think intention-to-treat should be considered in non-randomly assigned groups. Just thinking about a study of a programme to change behaviour (smoking). Group A nominated themselves for the programme, but 40 out of 50 of them did not complete it, it was sooo boring. It would be unfair to compare the 10 who did complete with the comparison group. The Intention-to-Treat principle is important because drop-outs skew your data, and if your intervention/drug is to be assessed comprehensively surely you need findings that account for the likelihood that people don't finish the intervention/drug prescription.