Try searching for 'Medicare' in Google, then opening another browser tab and searching first for 'Obama' and then for 'Medicare' again. Notice any difference?
Then try repeating the procedure with 'Romney' instead of 'Obama'.
The Wall Street Journal has done this as part of a commissioned study, and concluded that Google is customizing results for Obama but not Romney. Searching for 'Obama' changes subsequent results for 'Medicare', in a way that searching for 'Romney' doesn't.
There's a similar effect on searches for 'Iran', 'abortion', 'gun control' - and even 'iPhone' and 'sports'. Changes appear even when search history is turned off.
A Google spokesman told the Journal that it's simply trying to anticipate the wishes of the user. A search on 'Harry Potter' and then 'Amazon', for example, might indicate that the user might want to see Harry Potter products.
The difference in search results was first spotted by 'tracking-free' search engine DuckDuckGo.
"Sometimes tailoring can be good, e.g. we show local weather in our instant answer box. However, in other cases it can put you in a bubble, seeing more and more of what you already agree with, and less and less (relevant and important) opposing viewpoints. This effective filtering is troublesome when looking for raw information on a subject," says DuckDuckGo Gabrienl Weinberg in a blog post.
"For example, consider you're an undecided voter being bombarded with propaganda from both sides. What do you do to research the candidates? If you're like most people, you use Google as your starting point."
The changes apply only when a user has searched one one of what Weinberg terms 'magic keywords' - and while 'Obama' is one, Romney isn't. And while others include 'taxes', 'Ohio' and 'election', he says, 'Obama' transforms more subsequent searches than any other.
It's not clear how Google picks its magic keywords. While 'Romney' is searched on a little less often than 'Obama', for example, it's still more popular than, say, 'taxes'.
The altered results don't appear to show any political preference; indeed, when searching 'Iran' or 'gay marriage', each version shows both positive and critical coverage of both candidates. All the same, it's likely to trigger accusations of bias.