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Extent of personalization from browsing history for non-logged-in users

Ascertain the degree to which web search engines (specifically DuckDuckGo, Google, and Yahoo) personalize search result rankings based on a user's prior browsing history when the user is not logged in, and quantify how this effect varies across engines and query types.

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Background

Although search engines publicly state limits on personalization when users are not logged in, the authors emphasize that the role of browsing history in shaping search outcomes is debated. This uncertainty carries heightened importance for sensitive topics where tailored results could influence perceptions.

The paper’s audit finds signals that browsing history does influence results, but the precise magnitude and conditions under which this occurs remain unclear, motivating a focused determination of the extent of such personalization.

References

It is debatable the extent to which search-engines personalize the displayed content based on the user's past browsing experience, and the studied search engines claim not to do it as long as users are not logged in (Background and Table \ref{engines_policies}).

— Digital Gatekeeping: An Audit of Search Engine Results shows tailoring of queries on the Israel-Palestine Conflict (2502.04266 - Damião et al., 6 Feb 2025) in Section 4.1, Subsubsection “Does browsing history impact search engine results?”