The initial thesis is the starting point for your final thesis. The thesis in a research paper is supported by evidence and facts, not supposition. The preliminary thesis is bases on deductive reasoning, but the final thesis is a result of inductive reasoning.
A thesis in a research paper is a road map for your readers. It usually appears at the beginning of your first paragraph to guide the subsequent discussion that leads to the conclusion initially presented in the thesis statement. As you do your research the thesis statement will change and adjust to the facts. This one sentence statement guides the reader to a logical answer to the question asked in the thesis.
A good thesis statement in a research paper is deep but not wide. A weak thesis and rambling paper lacks the necessary structure. Write a few points and then one sentence from those points to pinpoint the thesis of your research paper. Economy of words ensures that your paper will have depth and focus.