Google search results used to be an impartial and objective list of the most valuable items they could find for a given query, based on factors like the number of links and the number of times keywords were mentioned in the text. However, as time passes, advancements are made in the way content is evaluated.
Nowadays, the world is much more complex. You have a lot of different valuations for content. For example, if someone does a search for “the best pizza”, what information do you think they’re looking for?
The intention of the user determines which of those three is most valuable, but it’s hard to determine what their intention is without context. That’s why Google encourages people to create accounts and to sign in. When you have an account, they can track details about you and your search history. They can track your location and other relatively anonymous information. That way, if you search for something generic like “best pizza near me” they can give you personalized recommendations for your precise location.
Here are all the factors that can go into personalizing your search results, and how signing in affects them.
The first major factor is your geographic location. Now, Google can get this information by default just from your IP address, but it’s a little non-specific. IP address can be off, or it can point to a subnet that is only as specific as your zip code. I’ve seen them pick up a city a few miles away from me as my location, for example. Also, if you choose to use a web proxy, it will give you completely incorrect information.
Signing in gives them the ability to more precisely track your location, particularly if you’re signed in on a mobile device – an Android phone or tablet specifically – and have high precision location tracking turned on. If you’re playing Pokemon Go you have that turned on for more responsive gameplay, so keep that in mind. Additionally, you can use your own custom location as part of your data, as precise as your street address. Using a mobile device, it can detect your GPS location if you have that enabled as well.
Location-based features in Google search are, obviously enough, most relevant to mobile users and most relevant to local queries. Queries like “where can I find a drug store” or “where is the nearest hospital” are local queries that benefit from having a precise location. Google will do their best to give you precise information for that on a desktop as well, but mobile devices offer both more precision and more need. When Google detects a mobile device, they are more likely to push local and mobile sites over general or national sites.
Google tracks your search history in a few ways. The easiest way for them is simply by account, of course, but if you’re signed out or don’t have an account, they will track it based on a combination of cookies stored on your computer, IP address, and browser user agent. Any one of those factors alone isn’t necessarily enough to positively identify you as a unique individual, but all of them combined give a good picture of a person’s search habits.
This allows Google to slowly customize your search results for certain types of queries. For example, the first time you run a search for mobile phone battery packs, they might present you with a handful of different results; a Shopping bar, an Amazon link, a Newegg link, a link to Anker, and so forth.
Now, say you click on the Amazon link. They don’t care what you do on Amazon, but if they notice you run another search for a product and click another Amazon link, a trend begins to develop. After a few more iterations, you might notice that the Amazon link is always #1 for product-related searches, and that more variations of the product on Amazon will show up in the first page of results. Meanwhile other vendors will drop down on the page or fall off it altogether.
If you have a Google account and are signed in, you can view the activity log they have compiled for you here, in the MyActivity section. You can change settings, stop records, delete individual entries, and other such management from there.
If you want to remove the customization and you’re not signed in, you will have to delete your browser history and cookies. This will start you from a clean slate, though they will build back up over time. Additionally, queries over 180 days old made while not signed in are deleted. This is the expiration for their cookie. Alternatively, you can use “Incognito Mode” or “Private Browsing”, depending on your browser, which will disable personalized search.
For more detailed controls, you can visit the activity controls page. This page has several sections for different types of activity. At the top is web and app activity, which is your search history and app usage, including mobile search, maps, and Google Now, among others. Next is Location History, which primarily applies to mobile devices and maps usage. Next is Device Information, which tracks what devices you use to access Google using your account, including desktops and mobile devices. Below that is voice and audio activity, which learns about your voice and accent to better customize Google Now (OK Google) to your personal use. YouTube search history and YouTube watch history are the last entries on the list.
When you sign in with a Google account, you also have the opportunity to somewhat customize your advertising preferences. You can report ads that you don’t want to see and you are tracked when you click ads, under the assumption that you don’t mind seeing them. Google is constantly categorizing your account by these actions.
Therefore, when you run searches, you see different sponsored results depending on various factors. One such factor is your personal activity. Much like on Facebook, you will see more content similar to what you have liked and clicked, and less of what you have ignored and reported.
Additionally, you will see different advertising depending on the time of the month or the year that you’re searching. Different companies run different ad campaigns for different lengths and different budgets, targeting different audiences. When the audience you’re a part of changes, or the targeting changes, or the ad budgets expire, the ads will change.
The device you use to connect to Google is having an increasing effect on search results. A few years ago, using a mobile device would only have a minor effect on local queries, based on your GPS location and little else. These days, Google has actually made mobile and responsive design for websites into a search ranking factor. If you’re using a mobile device to search, you are going to be shown more sites with mobile layouts than others. Sites without mobile layouts will still be shown if they are relevant, but they will be ranked lower, because they are harder to browse on a mobile phone.
There’s a small amount of integration with Google+ in search results, though it has been dwindling to almost non-existence. A few years ago, Google Authorship was the next big thing, and everyone was predicting it would stick around.
After a while, Google decided to reduce the preferential treatment they were giving to users of their social network. They dialed it back to just some personalized results based on if someone in one of your Google+ circles had written, published, or shared a given piece of content. It might show up with a little flag in the search results, or even their profile picture, though even those have died back recently. Still, Google+ integration may have some minor effect on the visibility of content produced by people you follow.
There are also some factors that can change your search results in broad strokes. By this, I mean from week to week, or from state to state. They won’t change much over the course of a day, nor are they likely to change when you travel across the city, unless your queries are relevant to an extremely local perspective.
The first factor is data center. Google has dozens of data centers around the world, serving geographically local searchers. Not all data centers are synced and alike. A website indexed in one data center might take a day or two to propagate amongst all of them. An algorithmic change is the same way. There will be some variance from center to center. However, you are pretty unlikely to experience this outside of cross-country travel, as the data centers tend to serve large geographic areas.
Algorithmic testing is another big factor. When Google is testing a new algorithm, like Panda, Penguin, Hummingbird, Pigeon, or a similar update, they start on small subsections of the population. Your search results might be different from someone else, for a short time before the algorithm is either reverted or is rolled out to everyone. In fact, the subset of accounts receiving changed results is how large companies like Moz measure incoming Google changes.
There are three ways you can test to see how different your search results are in different situations.
The first is to sign out of whatever Google account you’re using. I personally have four different accounts for different purposes – a throwaway account for signing up for offers, a business account, a more important personal account, and a fake account for testing. I can change my personalized results from account to account, or see what they track by logging out and running searches that way.
The second is to turn off activity tracking in the activity settings page I linked above. However, be aware that this method is a bit overkill; it will remove old data and cease tracking new data until such time as you enable it again. This gives you more objective settings, but also means local and personal results will be less effective or relevant for you.
The third method is to use incognito or private browsing mode in whatever browser you’re using. These types of no-tracking browser windows allow you to search without feat of being tracked or having those searches saved as part of your history. This is generally ideal for just one or two searches at a time.
You can also change your browser entirely for some differences, though changing browser won’t change results if you’re signed in to the same account. Likewise, you can delete your browser history, but that will only change your search results if you’re also signed out of your Google account; otherwise they’ll just use the data on their servers rather than the data on your computer.
Google’s major motto is to not be evil, but many people feel that the amount of data tracking Google does is firmly on the side of evil. They certainly use it, for a wide variety of reasons, including selling advertising and market research for themselves.
The trick is that personalized search is simply harvesting a lot of information you’re giving out more or less publicly. They give you controls to opt out of a lot of the tracking, so you only give them the information you really want to give them, outside of the bare minimum of tracking info you give everyone just by using the web. Quite frankly, you’re giving your ISP more information with less control than you are Google.
Plus, you’re getting benefit out of it. Personalized results may hide “objective” results, but ideally they’re giving you results you really would like to see. If you find that they’re getting in the way of your real target, you can simply disable the personalization. In the mean time, you can enjoy results tailored to your behaviors and your location in a way that is unprecedented in history.