A manual for writers of research papers, theses, and dissertations, 7th edition - Kate L. Turabian 2007

Sketch in the kind of evidence you should look for
Moving from a topic to a question to a working hypothesis
Part I. Research and writing: from planning to production

Every field prefers its own kinds of evidence—numbers, quotations, observations, historical facts, images, and so on. So for each reason, sketch the kind of evidence that you think you'll need to support it. Even imagine what the most convincing evidence would look like. If you can't imagine the kind of evidence you'll need, leave that part of the page blank, then read secondary sources to find out the kind of evidence that researchers in your field favor (see 3.1.2).