I'm applying for a job that asks for a writing sample in addition to a cover letter and resume. The bulk of my writing is research based and is an assignment from my MBA program. Isn't that going to be too long of a sample?
I would think that a "sample" would include a page or two of a few different writings. If they are getting a lot of applicants I'm sure they aren't interested in reading whole research papers. Imagine the stack!