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 third party cookies is easy to enable in either browser. Indeed, without a compact privacy policy then third party cookies are blocked by the default installation settings of Internet Explorer 6.

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.

JavaScript disabled

If JavaScript is disabled then the data that can be gathered is greatly reduced. Any form of tracking is likely to rely on 3rd party cookies or, at best, 1st party cookies. If JavaScript is disabled and cookies are blocked then it may be impossible to track a user’s journey reliably.

Although few home users block JavaScript, and in fact how to disable JavaScript is not entirely clear in IE, this is often the default setting on corporate computer installations to lower security risks.

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.

Blocked domain

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.

Reliance on cookies in web site user tracking

In the field of web analytics, one of the permanently hot topics is how to track a user’s activity on a web site accurately with the information that the technology available to us is able to provide. There are two main aims:

  • Tracking a user from their entry point into a site until they leave (known as a user’s ‘session’
  • Recognising the same user then they return to the site at some time in the future (to recognise them as a ‘visitor’)

This has been raised to the forefront again recently by Eric Peterson’s study for Jupiter that indicates that a high proportion of users (in the US, where the study was performed) regularly delete cookies from their computers.

Cookies are the principle, and still most reliable,form of tracking technology used by the major web analytics companies. These are used not only to track sessions, but also to recognise repeat visits by the same user.

If cookies are being deleted as regularly as the Jupiter report suggests then this would have the following implications for any web analytics that relies on cookie-based tracking:

  • If a user deletes a tracking cookie whilst in the middle of a session then their visit will not be tracked correctly, i.e it will be tracked. as two (or more) visits rather than one. Also, any conversions may be attributed to the wrong source.
  • If a user deletes a tracking cookie between sessions then they will not be recognised when they return to the site at a later date

Interms of what these would mean to site performance reports some of the following should illustrate why this is such an important issue for website owners:

  • Drop-off points will be incorrectly highlighted. Although this may not be statistically significant it will make it more difficult to identify trends.
  • The number of sessions reported will be higher than it is in reality
  • Conversion statistics may appear lower than they really are. One session may be incorrectly identified as two (or more), whereas only one will lead to a conversion
  • Conversions may then be assigned to the wrong source, possibly leading to incorrect decisions to abort or continue campaigns
  • Numbers of distinct visitors will appear higher than they really are
  • Repeat visits will appear lower, which may lead to unfounded doubts about the ‘stickiness’ of the site’s content.

The industry as a whole is trying to find ways to raise accuracy levels by other means but this brief look at the implications of cookie deletion when using a cookie-reliant tracking product shows what an important issue this is.

Jupiter study about cookie deletion rates

Nielsen Corroborates Jupiter’s Cookie Deletion Report

Clickz commentary on the jupiter report

Deleting page elements using removeChild in JavaScript

Here’s a handy(?) script to delete pieces of any page you’re on when you click on them:

javascript:document.onclick=new Function(‘e’,’document.all?;
src.parentNode.removeChild(src);return false’);void(0);

Go to any page on the web, paste it into the address bar of your browser and then start clicking around. It works okay in IE6 and Firefox – I haven’t tried it in anything else but it should be okay in IE5 (PC), and might work in Safari.

It uses JavaScript to access the DOM and then tells every element you click on to delete itself from its parent. Generally, a bit suicidal.

Try it out by clicking on this link and then clicking around on the page.