One of Google Analytics’ great features is that it can track visitors across multiple domains. This is especially handy for all those folks using a third party shopping cart. Getting GA configured correctly to work with a third party domain is not overly complicated but there can be some issues.

Here’s my list of the top mistakes made when working with a third party domain:

1. Missing GA tracking code

This is a simple step that many people forget. Make sure that you add the GA tracking code to all the pages on both domains. If the code is missing then the visitor will not be tracked. If the third party site does not allow you to add JavaScript to the pages then you may be out of luck.

Remember, the JavaScript code snippet needs to be modified slightly to look like this:

<script type="text/javascript">
  _uacct="UA-xxxx-x";
  _udn="none";
  _ulink=1;
  urchinTracker();
</script>

Don’t forget to replace “UA-XXXX-X” with your GA account number.

2. Missing __utmLinker() or __utmLinkPost()

The technology that GA uses to track visitors between multiple domains depends on two JavaScript functions: __utmLinker() and __utmLinkPost(). Both functions are included in the urchin.js tracking code. These functions transfer the GA tracking cookies from one domain to another via the URL. This is vital to identifying unique visitors and connecting which marketing activities lead to conversions.

Why do we need to transfer cookies between domains? Well, that’s a bit complicated and pretty technical. Think of it this way. Each visitor has their own set of cookies. For security reasons, we need a mechanism to transfer the cookies from one domain to the other. __utmLinker() and __utmLinkPost() are the mechanisms we use to transfer the cookies from one domain to another.

If you move visitors from one domain to another using regular links then you need to modify those links with the __utmLinker() function. Here’s an example:

<script type="text/javascript">document.write('
Log in Now');
</script>

<noscript>
Log in Now
</noscript>

If you move visitors between domains using a form, then you need to modify said form using __utmLinkPost(), like this:

<form action="http://www.mysite.com/process.asp" onSubmit="javascript:__utmLinkPost(this)">

How do you know if you’ve done it right? Go to your site and click on a link or form that drives the visitor from your site to the third party site. When you arrive on the third party site look at the URL in your browser’s location bar. You should see information like this:

http://www.cutroni.com/blog/index.htm?
__utma=var1&__utmb=var2&__utmc=var3&__utmv=var4&utmz=var5&__utmk=1232

The query string variables are the actual tracking cookies from the original domain. __utmLinker or __utmLinkPost placed them in the URL. When the visitor arrives on the third party site the urchin.js JavaScript will pluck them from the URL and create a set of cookies for the third party domain using the values from the URL.

3. Incompatible Architectures

If you’re banging your head against the monitor trying to figure out why GA is not working with a third party domain it could be that the third party site is not compatible with Google Analytics. This is very common.

First, the third party provider must let you add JavaScript to your pages. We discussed this above. No JavaScript tracking code, no visitor tracking.

Second, make sure the third party site lets you pass data to their site via the URL. Remember, that’s how __utmLinker() and __utmLinkPost() work. I’ve come across many third party sites that strip out query string variables which breaks the GA tracking.

To determine if the third party site is stripping out the query string variables use the method I described above. Go to your site and click on a link or form that drives the visitor from your site to the third party site. When you arrive on the third party site look at the URL in your browser’s location bar. You should see information like this:

http://www.cutroni.com/blog/index.htm?
__utma=var1&__utmb=var2&__utmc=var3&__utmv=var4&utmz=var5&__utmk=1232

The query string variables above (bolded) are the actual tracking cookies from the original domain.

If the third party provider’s architecture does not appear to be compatible with GA give them a call. Sometimes they’re willing to change. I’ve actually worked with quite a few vendors to help make their systems GA compatible.

Like this post? How about checking out these related posts:

1. How Google Analytics Tracks Third-Party Domains
2. Google Analytics Configuration Mistake #2: Query String Variables
3. Google Analytics Configuration Mistake #1: Missing Default Page
4. The Two Types of Google Analytics Configuration
5. Tracking Dynamic Sites With Google Analytics