Most users are unaware that personalised search even exists, let alone plays a part in hindering SEO efforts. For those of you that are, bear with me.
When you log into Google, for instance to access your Gmail, any searches you do are registered. This information is then associated with your account. Google uses this information to provide you with more relevant search results. For Joe Soap this is fantastic. It means that Google analyses your behaviour and is able to serve you better results from a Google search.
Even if you are not logged in to your Google account, any google searches can be associated with your computer. The results will not be quite as specific if, for example, you happen to share a family PC.
For those trying to work out how their SEO efforts are going personalised search is a disaster. This is because it skews results. For example, if I was to search for “SEO training” and click on this site while logged into Google, then Google would assume that this site interested me. If I do it more than once then it is reasonable to assume that this site is actually important to me. So Google kindly put this site at the top (or close to) of the search results it gives me the next time I search for “SEO training”. If I am looking for this page it is useful. If I am trying to see how well this site performs for the term “SEO training” then I am in trouble. I will incorrectly think that I am topping the charts for a keyword, when in fact, I am seeing different results to everybody else in the world.
If you want to check your rank in Google for a keyword you need to make sure that Personalised Search is turned off.
To turn off Personalised Search (Personalized Search) just follow the instructions posted by Google here.
Personalised Search has been in existence since 2007 and is turned on by default. As you can see it can lead to hugely misleading results if you are trying to measure your SEO effectiveness.