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Search engines are always biased, and there is no such thing as an unbiased search engine. It would be impossible to construct such a search engine, because human beliefs and assumptions influence the design of algorithms, and they therefore prefer certain documents to others. It is even at the core of every idea of ranking that, based on certain technically mediated assumptions, certain items are preferred over others.
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Dirk Lewandowski (2015) studied this question.
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