Use Web sites from reliable sources to supplement information you get from books and electronic texts.
When using Web sites, you need to be careful about quality and source. Ask these questions to help you determine whether a Web site is worth using for your paper:
If you do a Google search about your topic and some results come back from Google Books, you'll find that you aren't able to read all of the pages of the book online. Check the title of the book and look it up in our Library Catalog to see if we own it.
Web sites from government agencies are considered reliable and worthwhile investigating and citing, often for statistics. Cite the agency as the author in your reference list (as a "corporate author" rather than an individual person author).
Centers for Disease Control and Prevention
The MSU Libraries has another Guide for Finding Health Statistics and Data which points to useful sources for that kind of information.