Democratic presidential candidate Sen. Bernie Sanders speaks at a rally in Las Vegas last month. (AP Photo/John Locher)

Roughly three-quarters of Americans get their news online these days, making the Internet America's favorite news source, according to a 2014 Pew Research Center poll. And for many of them, their online news search starts with a Google query -- especially when it comes to news about campaigns and candidates.

But like any information source, Google's algorithm-driven search results aren't 100 percent neutral. Its search engine produces more favorable results for some candidates than others, new research has found.

In an analysis published by Slate, Daniel Trielli, Sean Mussenden and Nicholas Diakopoulos tallied the top 10 search results for each of 16 Democratic and Republican presidential candidates. Then they had a crowdsourced team of reviewers rate whether each of these results painted the candidate in a positive, negative or neutral light.

For instance, if the top search result was a candidate's own Facebook or campaign page, that would qualify as an overwhelmingly positive result. But if a news story critical of a candidate came up in the top 10, it would be coded as negative.

In they end, they found that "Democrats fared better than Republicans when it came to supportive and positive sites within the first page of results. Democrats had, on average, seven favorable search results in those top 10, whereas GOP candidates had only 5.9." If you chart the average Democrat and Republican favorability score in each of the top 10 slots, it looks something like this.


Daniel Trielli, Sean Mussenden, and Nicholas Diakopoulos.

As you can see, the average first result for Democrats is way more positive than the average first result for Republicans. And the last five results for Democrats are generally higher than for Republicans, too.

They focused on Google because it's the most popular search engine. But you could run a similar analysis for Bing, or even for searches on popular sites like Facebook and Twitter.

[Read more: How racism explains Republicans' rise in the South]

Does this mean Google is in the tank for Democrats? No. The authors say that the outcome is "an organic, emergent result constituted from a complex prism of quantification involving hundreds of signals and increasingly complex and opaque artificial intelligence." In other words, we don't know a whole lot about Google's algorithm. But we do know that pages that get a lot of traffic or are frequently linked to on other websites tend to do better in the rankings.

That helps explain why Democratic presidential candidate Sen. Bernie Sanders fares so favorably in Google searches -- nine of his top 10 results were rated "very pro" in the analysis. The senator from Vermont has a strong social media presence and a lot of followers on multiple platforms. So his Facebook, YouTube and Twitter accounts all come up high in the search results, contributing to an overall positive result.

GOP candidate Sen. Ted Cruz (Tex.), on the other hand, has a more muted social media profile, so only his Facebook account shows up in the top 10. He had as many negative as positive results on his search page, with three of his top 10 results rated "very con."

Republican candidate Donald Trump also had an equal number of negative and positive results, not surprising given all the bad press he's received lately.

In fact, Sanders is a big outlier when it comes to the positive tone of his search results. And since there are only three Democratic candidates, the higher Democratic values in the chart above are in many ways a reflection of this.

Still, the piece is a good reminder that a lot of complicated factors go into determining what shows up on our search pages, and that many of us don't give them a second thought as we search and click through. Research has consistently shown that "Internet search rankings have a significant impact on consumer choices" -- and this is just as true in politics as it is in other fields.

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