The effects of browser settings on web analytics
Modern web browsers give the user some degree of control over their privacy and security settings. These can have a major impact in trying to measure how web site's are used either through preventing web analytics products from registering the user at all or by altering the way data is captured such that the information is unreliable.
The most common two browsers at present are Microsoft's Internet Explorer (IE) version 6 and Mozilla Firefox. IE currently has by far the larger share but Firefox is growing with around 10% at present and so is becoming statistically significant.
Each of these allows control over browser settings to similar effect, although how these are configured is different in each case. It's fair to say that Firefox allows slightly more control whereas IE presents the controls in a more 'user friendly' way. However, many of the main features are the same in both.
Taking the options available to the user in turn, below is a summary of the effect that these may have on web analytics software.
Blocking 3rd party cookies
If tracking of users and recognising them even within a single session requires 3rd party cookies to be enabled then a session will appear as multiple sessions in any reports.
Blocking 1st party cookies
1st party cookies are much less likely to be blocked than 3rd party cookies. However, the effects on the ability to track visitors if they are blocked is the same as with 3rd party cookies.
Blocked 3rd party images
Most web analytics products communicate data to the tracking server by dynamically writing an image tag into the page to be tracked. This image tag is generally located on the server of the analytics company and hence is 3rd party. If 3rd party images are being blocked (as it is simple to do in Mozilla Firefox) then no data at all will be received by the tracking server.
IE does not have a way for users to enable the blocking of 3rd party images but this option is presented on the same page as blocking cookies within Firefox's preference settings.
Even more severe than blocking 3rd party images, it is possible to block an entire domain meaning that any requests to it are blocked. In this case, even if the analytics information is passed to the tracking server by a method other than an image then the server will not receive it.
The blocking of domains is commonly achieved by installing a file known as the 'hosts' file in a particular folder within the Microsoft Windows operating system. These hosts files, containing common ad servers and analytics company's domains, are readily available for download from the internet.