I wrote in my dissertation draft (Version 1037.2) that the reason I was surveying students about their experience of initial assessment was because I thought that they were more likely to give candid responses than their lecturers.
I beleive that academic staff would have answered my questions about assessment based on; what they think they should say, what their organisations policy says is done, and what they think they've done. Whereas a student would say; "we did this" or "we didn't do that".
Now of course I have to find some evidence to back up my assumption.
