A slight change in approach

I'm starting to think of methodologies that will work with my research on students and self-efficacy. I looked up several sources on self-efficacy since not much has been done on GSP by itself. Self-efficacy is interesting but I'm having trouble redesigning my research question to include my thoughts on it. Right now I have several ideas, in no particular order in my head that I'm struggling to define and/or organize for my proposal.

Will students with low self-efficacy in writing place themselves in English 120?
Will students with high self-efficacy in writing place themselves in English 121?
What are the implications if the answers are yes to both questions?

How will I determine what is considered low and high self-efficacy? I think this is something I will determine by modifying what previous researchers have done to measure high and low self-efficacy. Most seem to resemble a questionaire/survey format. Once I determine who has high writing self-efficacy and who has low writing self-efficacy I can maybe interview a couple students from each group to find out more on why they enrolled in English 120 or English 121. This would give me a better idea of where they are coming from and whether we should compensate for self-efficacy in addition to placement decisions based on the GSP questionaire. Something tells me the questionaire is not enough by itself. Do we need a small form of checks and balances, or does that undermind our students' rights to place themselves in composition courses? I feel like I'm running around in circles...am I thinking too big for this sort of project?