The world is full of information, however, all information is not correct.
Evaluating the source is an important research tool you can use to make sure the information you are getting is reliable.
Characteristics of valid sources:
The information is reviewed by qualified individuals who agree that the information is true.
The source has a long history of providing accurate scientific information.
The source is not paid for by a company or organization that would want to control the results.
The source provides direct evidence or first-hand testimony. A source that isn't primary could provide anecdotal evidence. Anecdotal evidence might provide information based on non-scientific observations or studies.