Use primary sources whenever possible. For example, if you're writing about Jane Goodall, using Goodall's books and publications is better than relying on another author's book about Goodall's work. If you're writing about scientific research, read the actual studies, not just commentary on the studies. Secondary sources add bias and commentary to primary sources, making them less reliable. They may also misrepresent the meaning of the original author's words. However, secondary sources can provide useful information about how critics have interpreted a primary source.
The importance of a source's timeliness depends on your topic. For example, if you're writing about contemporary topics, such as current foreign policy or cutting-edge medical research, you should use recently published references because older references may be out of date. However, reading older studies can help you understand the foundation for recent research. If you're writing about philosophy or literature, for example, older sources are still relevant and acceptable.
Peer-reviewed or refereed sources, such as peer-reviewed academic or trade journals, are more reputable and authoritative than sources that have not been peer reviewed. During peer review, other scholars in the article's field examine the article before it gets published. This process ensures the articles are credible.
If you're writing about a topic that has several perspectives or opinions, read a variety of opinions and acknowledge them in your paper. For example, if your paper is a persuasive essay about gay marriage, refuting common arguments against gay marriage will make your paper stronger. Searching for "cons of gay marriage" as well as "pros of gay marriage," for example, helps one find a variety of sources. Avoid sources that use emotional language or rely on opinions instead of facts because these sources are less reliable.
Writers shouldn't use blogs, personal websites, journals that haven't been peer reviewed or websites that contain user-submitted content for their research. These sources are typically not written by experts and may include inaccurate information. If you find interesting information or ideas on these sites, you can locate the original research or study referenced by these sources. Most website articles list original studies or primary sources.