Further, unbiased articles may easily contain biased words. Especially since Wikipedia is an international projects, the articles describe multiple points of view, and the "code words" of the research were terms such as the following: "tax breaks, minimum wage, fuel efficiency [--] death tax, border security, war on terror".
I'm not sure that's a great measure of bias. It's easy to write in an unbiased tone, yet still be biased.