Run every source through the CRAAP test below: if you find you cannot answer some of the questions or the answers come up negative, then the source is probably not trustworthy.

Currency

When was the source published?

Has the issue changed much since then?

Relevance

Does the source speak to your topic?

Authority

Who is the author?

Why do you trust them? Do they have experience in the field or a degree that qualifies them to speak on the subject?

Accuracy

What kinds of evidence are used to support the source's arguments?

Are citations, research, or statistics used?

Purpose

Does the source exist to further a biased point of view?

Is advertising present? Or is the source non-profit?

There are a number of good clues that tell you whether a source is worth using:

• Are there numerous references at the bottom?
  
  
• Is the author clearly identified? Do they hold an advanced degree?
  
  
• Are statistics and research used, not just opinions?

If all of those are true, you are probably looking at a good source. On the other hand, sources with no citations that offer only opinions are not worth using.

Good: Genetic Diversity of Potato virus Y Complex

Currency: published February 2013

Relevance: pretty good if you're researching potato viruses

Authority: one author is a professor, the other works for the Department of Agriculture

Accuracy: many references, schematic diagrams

Purpose: non-profit research, though there is an ad on the side

Questionable: Potato Goodness Unearthed

Currency: can't tell when content was written, no publication dates

Relevance: just gives general potato information, nothing specifically on diseases or viruses

Authority: can't tell who writes the content

Accuracy: facts are stated but no citations, can't be verified

Purpose: the site is essentially a pro-potato lobbying organization which would have an interest in concealing negative aspects of potatoes (e.g. diseases or unhealthiness)