Thank you very much for your detailed response. I am not saying " I am right" - I just feel I need to search the literature to back up his ideas but the literature doesn't... I told him in a nice way but he is stubborn and laughs it off. He is very nice but it makes me feel I have to find what he wants me to find..

So I am doing a feasibility study for my PhD and have to design and then deliver an intervention to a group of parents. My supervisor wrote the bid for which we received the grant. He seems to think that what he wrote in the initial bid is the only way to go (making me sometimes feel like a research assistant but that is another issue). After 7 months of lit review, talking to key stakeholders etc it seems that his proposed idea of 16 people in an intervention group with just me as the facilitator is not quite a good idea ( politely) - everything and everyone suggest groups of 7. He just won't listen to me or the research and said there is no evidence to suggest the opposite... I seriously don't know how I am going to do it but also feel it is MY phd and I feel I constantly have to do things that were his idea.. . I know I am in receipt of a scholarship but I find it hard to deal with this. ANy advice on dealing with a stubborn supervisor or even better to suggest that group sizes over 7 are a bad bad idea.....?