Consider a Source's Degree of Specialization
Some sources are considered to be general; that is, they are written for a general-interest audience. Newspapers and popular magazines typically provide general information about a topic or issue. In contrast, highly specialized publications are written for specific, specialized audiences such as microbiologists, mortgage bankers and auto mechanics.
General sources can be helpful as you begin your research, but as your project develops you may need the deeper authority of specialized sources to provide the latest information on your topic. Keep in mind when using extremely specialized works that you may get people in over their heads. Be sure to explain information that your audience needs to understand if they are to grasp the conclusions you arrive at in your paper.