How you evaluate a source will differ depending on the project you’re working on. When determining whether a source is credible, biased, or relevant, it is equally important to consider how the source will be used.
For example, Phillip Morris has a website that touts the company’s programs to curb smoking among young people. Obviously, information from a tobacco company and cigarette marketing giant can be considered biased. You must ask yourself whether their program is effective and whether the content of the site can be trusted and in what context.
Should you never use that source? You might want to if you were writing a paper that examined the smoking rates of 10-13 year olds. What role might the Phillip Morris site play in your paper? Does the site display information that contradicts the company’s advertising campaigns? Would the campaign website be effective in your argument? It all depends on what side of the argument is going to be supported in your research project.
Audience. Purpose. Argument. These intents should be considered since they affect how sources should be evaluated.