Text similarity in academic conference papers

Abstract

If we are to use electronic plagiarism detectors on student work, it would be interesting to know how--much similarity should be expected in independently written documents on a similar topic. If our--measure is coarse, the answer should be zero, but a finer grained analysis (such as would be needed to--detect inadequate paraphrasing) is likely to detect some background noise. How much background--noise should there be