Wednesday, April 4, 2007

Instances vs. Visits in Omniture

An interesting question was posted to the Web Analytics forum: why is Omniture reporting higher referral instances than visits to a site?

What is a visit?

Omniture says "a visit is a term that refers to a visitor’s access to a website. The visit begins when a person first views a page on your company's website. It will continue until that person stops all activity on the site for 30 minutes." You might want to view my previous post on the atoms of web analytics.

What is an instance?

Again, Omniture says "an instance as relates to the number of times that a unique event occurs in SiteCatalyst". First, I wouldn't say in "SiteCatalyst"... the event occurs on my site, but that's a detail. An instance = count of event.

The counts doesn't match up!

In the screen snapshot above, the number of visits is 62,013 while the number of instances for 87,444... How can SiteCatalyst register 41% more instances than visits? But wait! We're not measuring apples with apples. Instances and visits are two different measurement units.

Let's do an example

Nothing better than an example to demonstrate the difference.
TimeUser activityVisitsInstances
8:00pmA visitor goes on Google and do a search for "web analytics".

8:01pmThat visitor click on a link to ""
+1+1 from Google
8:05pmThe visitor browse a few pages and leave my site.

8:06pmThe visitor goes back to Google and do a search for "Omniture 3rd party cookie" and find the second entry to be an article from my site+0+1 from Google
8:15pmThe visitor does a "back" and look for other results from Google, than find the fine piece about "Web Analytics technical implementation best practices".

8:30pmAfter reading the article, the visitor look at the comments. One of them links to my site+0+1 from
9:30pmThe visitor leave for more than 30 minutes since the last hit to my site, then come back and click on my home page link.+1

End result:2

Hope that helps!