If several people do a web search for exactly the same term e.g.. “Restaurants Reading”, you’d imagine that they should get the same results. But no, that’s not how Google works.
It will always provide a personalised search based on your location, web history, and browsing habits to customise your search results.
Location
Google attempts to auto-detect your IP address. If you use Google Chrome, or have the Google toolbar, there is a feature called “My Location” – This tells Google exactly where you are. (You can even be seen on Google Maps).
So if two individuals do a particular search on Google.de, one in the UK and one in France, the IP addresses are so far apart, searches will most definitely be different. They would also be using different Google data centres. (details on that below).
Web History, Browsing Habits
Google will use browsing history to try and predict the results we may prefer. For example if two people search “Restaurants Reading”, and one has looked up Chinese Restaurants in the past, whereas the other has spent more time considering Mexican restaurants, the respective browsers will each be loaded with these past preferences.
This will result in the first person seeing higher rankings for Chinese restaurants, and the second seeing more results for Mexican restaurants – even under the same keyword search. The results are personalised by Google, even though those restaurants may have spent time and energy trying to get the best possible SEO rankings.
On top of all this, there is now a new feature called “Personal Results”. If you have a Google account, like Google Plus, and browse while logged in, your results will be even more filtered down.
Google Data Centres
This is where it gets a bit tricky. The keyword search that you do is performed by a Google data centre based on your IP address. There is no information on where they are, or how many there are. While the search term will be the same, the mathematical algorithm used will have a slight variance. So basically if I search “restaurant” right now, Google may go to a data centre based up in Scotland, while someone else’s may go down south – and this differs the results.
Algorithm testing
This is the formula Google uses to show results. This actually changes based on users. 40% of searches will differ slightly. You will see different results than your co-worker – even if you are both logged out of Google, have just cleared your cookies, and are searching from the same IP address.
Many searchers do not even realise that the results they receive have been modified. Personalised Search affects everything we Google and it’s very difficult to avoid it altogether – but the good news is that it can be controlled to a degree with opt out options. To get an unfiltered view you can delete your Web History and even turn it off completely.