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

Evaluate the reliability of print sources
Finding useful sources
Part I. Research and writing: from planning to production

You can't judge a source until you read it, but there are signs of its reliability:

1. Is the author a reputable scholar? Most publications cite an author's academic credentials; you can find more with a search engine. Most established scholars are reliable, but be cautious if the topic is a contested social issue such as gun control or abortion. Even reputable scholars can have axes to grind, especially if their research is supported by a special interest group.

2. Is the source current? Many reputable scholars write books and articles popularizing the research of others. But by the time you read them, these tertiary sources may be out of date. How fast a source dates varies by subject, so check with someone who knows your field. For journal articles in the social sciences, more than ten years is pushing the limit. For books, figure fifteen or so. Publications in the humanities have a longer life span.

3. Is the source published by a reputable press? You can trust most university presses, especially those at well-known schools. Before they publish a manuscript, they ask experts to review it (a process called peer review). You can also trust some commercial presses in some fields, such as Norton in literature, Ablex in sciences, or West in the law. Be skeptical of a commercial book that makes sensational claims, even if its author has a PhD after his name.

4. Was the article peer-reviewed? Most scholarly journals, both print and online, publish only peer-reviewed articles. Few commercial magazines use peer review, and fewer still check an author's facts. If a report hasn't been peer-reviewed, use it cautiously.

5. Has the source received good reviews? If the source is a book published more than a year ago, it may have been reviewed in a journal in the field. Many fields have indexes to published reviews that tell you how others evaluate a source. (See the bibliography.)

6. Has the source been frequently cited by others? You can roughly estimate how influential a source is by how often others cite it. To determine that, consult a citation index (in the bibliography, see section 4 in your field).

Those signs don't guarantee that a source is reliable, but they should give you reasonable confidence in it. If you can't find reliable sources, acknowledge the limits of the ones you have. Of course, you may find an exciting research problem when you discover that a source thought to be reliable is not.