As you do research you should always be alert for bias (prejudices or preconceived notions that may color the author's arguments). Follow these guidelines to detect bias:
Author information -- What does the author tell you about herself? Is she a member of an advocacy group? Is she linked to a business or political organization?
Language -- Does the author use pejorative terms? Does he use hyperbole? Or does he present facts without strong language?
Evidence -- Does the author cherry pick facts? Look for omissions in the data, for example showing research from 2006 and 2010, but skipping the intervening years. Is the coverage in-depth or does it only cover one side of the issue?
Images -- If there are images what do they depict? For example a peaceful protest vs. an angry mob.
Source: Kirszner, L. G. & Mandell, S. R. (2014). Practical Argument: A Text and Anthology. Boston: Bedford/St. Martin's.