For writing guides on persuasive or argumentative styles of writing, see the OWL Writing Center web site from Purdue University:
Evidential support (whether factual, logical, statistical, or anecdotal). The argument essay requires well-researched, accurate, credible, detailed, and current information to support the thesis statement and consider other points of view. Some factual, logical, statistical, or anecdotal evidence should support the thesis. Consider multiple points of view when collecting evidence. In text source citations are required along with a Work Cited page. Remember sources cited within text must also be listed on the Works Cited.