The OWL at Purdue: The world is full of information to be found—however, not all of it is valid, useful, or accurate. Evaluating sources of information that you are considering using in your writing is an important step in any research activity.
The quantity of information available is so staggering that we cannot know everything about a subject. For example, it's estimated that anyone attempting to research what's known about depression would have to read over 100,000 studies on the subject. And there's the problem of trying to decide which studies have produced reliable results.
Similarly, for information on other topics, not only is there a huge quantity available but with a very uneven level of quality. You don't want to rely on the news in the headlines of sensational tabloids near supermarket checkout counters, and it's just as hard to know how much to accept of what's in all the books, magazines, pamphlets, newspapers, journals, brochures, Web sites, and various media reports that are available. People want to convince you to buy their products, agree with their opinions, rely on their data, vote for their candidate, consider their perspective, or accept them as experts. In short, you have to sift and make decisions all the time, and you want to make responsible choices that you won't regret.
Evaluating sources is an important skill. It's been called an art as well as work—much of which is detective work. You have to decide where to look, what clues to search for, and what to accept. You may be overwhelmed with too much information or too little. The temptation is to accept whatever you find. But don't be tempted. Learning how to evaluate effectively is a skill you need both for your course papers and for your life.
When writing research papers, you will also be evaluating sources as you search for information. You will need to make decisions about what to search for, where to look, and once you've found material on your topic, if it is a valid or useful source for your writing.