Political bias on Wikipedia: in the eye of the beholder?

Earlier this week, The Daily Dot reported on a new study that found Wikipedia has become less politically biased over time, at least where U.S. politics are concerned. The study contrasts with previous data such as mid-2012 research by Engage DC which found that Wikipedia was slightly skewed towards liberal viewpoints.

Researchers Shane Greenstein and Feng Zhu analysed over 70,000 Wikipedia articles for phrases that indicate either Democratic or Republican bias including "Obamacare," "civil rights" and "illegal immigration". Their findings indicated that since 2001, Wikipedia has become more neutral as a wider range of editors have become involved in the project. Versions of articles from Wikipedia's early days in 2001 tended to be slanted towards Democratic viewpoints. More recently, their analysis found Wikipedia shows a balance of views.

However, the findings come with a caveat: it may be that increase in the overall number of articles is balancing out the encyclopedia's political leaning, such that overall the site is less biased, but individual articles could be slanted to any particular viewpoint.

The new research is particularly interesting coming after heated debates on Wikipedia in 2012 over bias in political articles. For instance, on the Paul Ryan Wikipedia article, editors clashed over perceived bias on both sides: arguments arose that detractors were adding negative information, while at other points editors argued there was too much "puff" being added. Around the same time, Wikiproject Conservatism came under fire from some editors for perceptions that its members had been attempting to insert Republican viewpoints and counter liberal views in political articles. More recently, questions have been raised about "whitewashing" of controversies from Senator Elizabeth Warren's biography.

Could it be that political biases vary by article, or perhaps such bias is in the eye of the beholder?