Now that you have found a variety of sources that support your thesis, it is time to evaluate them to select the ones you want to use. You want to assess each source using the the elements of the RADAR test, the criteria of your assignment and the combination of content that will enable you to tie all the pieces of your topic together in your paper.
Any source whether it be a book, article, oral history, website, piece of art, etc. can be biased which is why good researchers always question everything they see/hear. It is always important to evaluate all of the resources you find during the research process to determine their level of objectivity/subjectivity and to identify any biases. Doing this will help you determine which resources are the best for your paper or project.
Objectivity: Striving (as far as possible or practicable) to reduce or eliminate biases, prejudices, or subjective evaluations by relying on verifiable data. [BusinessDictionary. Retrieved from http://www.businessdictionary.com/definition/objectivity.html]
Subjectivity: Refers to how someone's judgment is shaped by or based on individual personal impressions, feelings, and opinions rather than external facts. [Vocabulary.com Dictionary. Retrieved from https://www.vocabulary.com/dictionary/subjectivity]
Bias: An inclination or outlook to present or hold a partial perspective, often accompanied by a refusal to consider the possible merits of alternative points of view. It is often one-sided, lacks a neutral viewpoint, and ignores or distorts any facts and verifiable data that is contrary to that person's perspective or belief. Biases can be learned implicitly within cultural contexts. People may develop biases toward or against an individual, an ethnic group, a nation, a religion, a social class, a political party, theoretical paradigms and ideologies within academic domains, or a species. Biased means one-sided, lacking a neutral viewpoint, or not having an open mind. Bias can come in many forms. [Wikipedia. Retrieved November 17, 2016 from https://en.wikipedia.org/wiki/Bias]
Ask yourself the 4 W's: Who, Why, When & Where