Because the argument, information, project, etc. on which you are working is only as strong as the evidence you bring to it. Your writing or presentation takes on the "character" of your sources.
If you use unreliable sources, your own paper will be unreliable and unbelievable.
In most cases, you are not an expert. So to be believable to your readers, you must bring to your paper (& other projects) the opinions and research of experts. Such sources are written by the experts themselves or rely on expert opinion/research for their content.
The stronger your evidence, the better your presentation will stand up to critical judgment by your professor. Therefore, selecting high quality information is extremely important.
Source:Beck, Susan. The Good, The Bad & The Ugly: or, Why It’s a Good Idea to Evaluate Web Sources. 1997. Revised 2009 version.
Accuracy -- is the information reliable and error free?
Is there an editor or someone who verifies/checks the information? Is it peer-reviewed?
Is there adequate documentation: bibliography, footnotes, credits, quotations?
Are the conclusions justified by the information presented?
If you are unable to verify accuracy based on these 3 bulleted items, look outside the source itself (do additional research): Is the information verified in other sources? Do experts agree on the findings?
Authority -- Is the source of the information reputable?
What are the author's qualifications? staff reporter? scholar in field?
How did you find the information? Did you use an index or references from other works?
What type of source is it? Sensationalistic? Popular ? Scholarly?
What is the reputation of the publisher?
If no individual is taking responsibility for the article, who is?
Evaluate the publisher's reputation for guaranteeing accuracy. (If no author is given on a web page, is the sponsor of the page reputable? If the sponsor is also not indicated on the web page, can you determine its origin from the URL and digging deeper into its website)
Objectivity -- Does the information show bias?
What is the purpose of the information? -- Inform? Persuade? Explain? Sway opinion? Advertise?
Does the source show political or cultural biases?
If you are unable to determine objectivity based on the bulleted items above, look outside the source (do more research): Do other sources provide other viewpoints?
Currency - When was the information published? When was the information collected?
Is it current?
Does it reflect the time period about which you are concerned?
Coverage -- Does it provide the evidence or information you need?
Is the audience for which it is intended appropriate for your purposes? (professional, layperson, child, adult?)
Is it suitable for your level of understanding? (too simple, too difficult?)
Is the information in the appropriate format? (print, electronic, video, sound?)
Does it cover the topic(s) you need? Does it provide the main points or concepts you need? Do its major findings add to your understanding? Do they support or refute your original ideas on the topic?
Evaluate health and medical information carefully.
See: Evaluating Health Information, provided by the National Library of Medicine and the National Institutes of Health. Websites should be transparent about their sources of health information. In an effort to improve health information on the Internet, the Health on the Net Foundation has a set of honor code principles for websites to follow.
Read article: This study by Hasty, et al. that concluded "most Wikipedia articles for the 10 costliest conditions in the United States contain errors compared with standard peer-reviewed sources." [Hasty, RT, et al. (2014). Wikipedia vs peer-reviewed medical literature for information about the 10 most costly medical conditions. Journal of American Osteopathic Association, 114(5),368-373. DOI: 10.7556/jaoa.2014.035.
