Wikipedia: Evaluating Wikipedia

Wikipedia articles are not equal in quality, scope, and depth. Because (1) it is a collaborative project and (2) the extent of human knowledge is always changing, the quality of Wikipedia articles range from "Stub" (or placeholder) pages, to pages of poor quality, to pages of high quality. You can determine the quality rating of any article by viewing its Talk page. To learn more about Wikipedia's Quality ratings, see its Grading Scheme.

In general, high-quality articles have five elements:

• a lead section that gives an easy-to-understand overview, 
• a clear structure, 
• balanced coverage,
• neutral content, and 
• reliable sources.

Source: Evaluating Wikipedia

In general, low-quality articles:

• have a warning banner at the top,
• show signs of language problems in the lead section,
• contain unsourced opinions and value statements,
• refer to “some,” “many,” or other unnamed groups of 
  people,
• seem to be missing key aspects of the topic,
• have some sections that are unnecessarily long,
• lack or have very few references and footnotes,
• have Talk pages filled with hostile dialogue.

Source: Evaluating Wikipedia

Bias and controversy exists wherever groups of individuals are involved and Wikipedia is no exception. In fact, Wikipedians have compiled a list of examples from their own history: 

Every version of the article from its creation to its current state is saved: and you can see every edit ever made by selecting the View History tab at the top right of each Wikipedia page. Take a look at this page and ask yourself:

• When was the page created? How recently was it edited? How frequently is it edited?
• How many people have edited the article? Is it the work of a few authors or many authors?
• Is there evidence of editing wars, repeated vandalism or reversions, or arguments?

Some articles are more difficult to write than others. This is especially true for controversial topics, current events, and quickly changing or emerging fields of knowledge. You can learn about the deliberations behind the creation of an article by selecting the Talk tab at the top left of each Wikipedia page. Take a look and ask yourself:

• Do people have doubts about the validity of the article or the way it is written?
• What aspects of the topic appear to be in debate?

A well-written Wikipedia article is a well-researched one. The authority of Wikipedia rests in the nexus between collaborative work and trustworthy sources of information. Even so, you should be critical of the References listed at the bottom of each article and ask yourself:

• How authoritative are the works cited? Are they scholarly books and articles? Popular news websites? Personal websites?
• Do most of the citations come from a single source or are there a variety of sources?
• When were the cited sources published (and how does that relate to the currency of the topic)?

Additionally, well-research articles will often contain a Bibliography-- a list of additional resources for people seeking more detailed information, a See Also section that allows readers to explore tangentially related topics, and an External Links section for locating additional (often more current) information outside Wikipedia.