The evaluation of information is an essential part of information seeking process. You should always evaluate the information you’ve found with following guidelines:
Relevance. Is the information suitable for your subject?
Currency. Is the information up-to-date?
Source. Who has written or has produced the information?
Truthfulness. Can you trust the information?
You should strive to use scholarly literature as source when writing a thesis. Being able to identify different types of publications, for example scholarly publication vs. popular publication, is an important skill to learn. Popular publications include magazines, newspapers and trade journals.
What is a scholarly article?
Primary sources or original sources provide new information and give direct evidence on a topic. Primary sources include for example research articles and dissertations, where authors report their own research and its findings.
Secondary sources or second-hand sources discuss primary sources. Secondary sources comment, evaluate or summarize on a research, or draw conclusions from them. Secondary sources include for example news articles on a research, literature reviews and textbooks.
You should use primary sources whenever possible. Secondary sources include analysis and interpretation, which may distort the contents of the primary source. This doesn’t mean secondary sources are unusable, but you should consider their usability along with other criteria. Good secondary sources are for example a literature review published in a scholarly journal, where they draw together a number of research findings to summarize current knowledge on a topic or an article where the author summarizes the findings in his or hers dissertation.