Primary sources are original research experiments that publish the results or findings in scholarly journals. High-quality articles go through a peer-review process before being published. When your professor asks you to use primary sources it means they expect students to search for and analyze original scientific research.
A secondary source means the author(s) are writing about others’ research. Thus the research is secondary because it is a second-hand translation of original research. Secondary sources include encyclopedias, dictionaries, textbooks and review articles where the author analyzes and critiques others’ original research articles. Secondary sources can be high-quality scholarly publications that provide background information on a topic. They are an excellent starting point when learning about a new topic.
An overview source is a kind of secondary source that provides a "big picture" understanding of a given topic.
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