Which sources are most reliable?
High Quality Sources
Examples: Scholarly books, articles in scholarly journals, trade books and magazines geared towards an educated general audience (e.g. Nature or Smithsonian), government documents, or textbooks and reference books.
These sources provide in-depth information. They are researched and written by subject matter experts and are carefully reviewed.
Varied-Quality Sources
Examples: News stories and feature articles from reputable newspapers, magazines, or organizations (e.g. Newsweek or PBS); documents published by businesses and nonprofit organizations; book reviews.
These sources are often useful. However, they do not cover subjects in as much depth, and they are not always rigorously researched and reviewed.
Questionable Sources
Examples: Loosely regulated media content like internet discussion boards, blogs, free online encyclopedias, talk radio shows, television news shows with obvious political biases, comment sections, or personal websites.
These sources should be avoided. They are often written to attract a large readership, present the author's opinions, or cause a reaction, and they are not subject to careful review.
How to evaluate
If you're trying to decide whether a research article is actually relevant to your topic, don't read the entire thing just yet. Start with the abstract, the introduction, and the conclusion--that's where the most important information will be mentioned.
If the conclusion discusses something that fits your topic, it's worth reading more, but you haven't wasted all your study time on irrelevant sources!