Evaluating Research:
Date of Publication
There is no magic number of years you can use to judge whether or not a source is current. Although it was published in 1859, Harriet E. Wilson's, Our Nig, is still current if you were interested in the lives of free blacks in the north just prior to the Civil War. However, it would not be current if your subject was African-Americans in the 21st century. Scientific and medical publications lose their currency quickly. If you are not sure if a resource is current, ask your instructor for assistance.
Discussion
Too often, students incorrectly assume that any book they find in the library is useful for their research. Unfortunately, this is not true.
When Larry Siegel and Milan Korcok published AIDS: The Drug and Alcohol Connection in 1989, it was celebrated because it provided important information in terms that non-medical professionals could understand. Yet, if you were writing a paper on contemporary AIDS issues, you could lose credibility as an author if this book appeared in your bibliography.
Our understanding of AIDS has changed so significantly since 1989 that what was up-to-date and factual then might be totally discredited today. However, Siegel and Korcok's book might have a place in a contemporary paper if it were being used to give an historical perspective, to demonstrate when a concept was first introduced, or to compare changes in knowledge over time.
Special Notes on Web Pages
Many web pages do not include the date when they were last updated. You need to be skeptical about using the information found on such pages.