I would like to emphasize that the sooner you start working with a statistician during the development of your proposal, the smoother things will go for you. Once you have a topic and you have done some preliminary literature review is an ideal time to start working with a statistician.
So many of my clients come to me only after multiple rewrites of the problem statement, research questions, data analysis plan etc. They could have saved themselves a lot of time, money and frustration by contacting a statistician sooner.
In addition, many of my clients come to me only after they fully approved proposal. Often times, a proposal is accepted even though the statistics are not clearly written and sometimes, their statistics are just plain wrong. This can happen if you don’t have someone with an advanced degree in statistics on your committee. When that happens, I am unable to do the analysis for them unless we first redo the statistics in the methods chapter.
Another thing that happens is, the student comes to me with a fully approved proposal and they want help with the analysis. The statistical aspects of their methodology are correct, but unnecessarily complicated that I am unable to help them due to the scope of the project being so large I could not fit the work into my schedule, nor could I do the work for an affordable price.
These are some of the reasons why you want to work with a statistician early in the development of your proposal.