Omniture - Instances, visits and pageviews

I always wondered what is the difference between these metrices in SiteCatalyst. Are these just different terms for same data or different data. All my theories started failing when I actually looked at the data in different reports. Are Instances, pageviews same - quick answer is yes but then why the data is different for same date range. Phew!! I was almost lost and then thought of getting answers to these before moving further!! 


First we will talk about the basic definition and then answers to some of the common observations.

Instances - Instance is primarily used in reports in Traffic Sources menu. An instance is counted for number of times a particular value is received in SiteCatalyst. For example, in Referrers report, if a user clicks on the link on a link on google and comes to your site, then for google as referrer one instance is added. If the same user again goes to google and clicks to come to your site irrespective of session, then the instance is incremented further.

Visit - Visit is counted once in a session irrespective of how many times you view a page. For referrer report, if a user comes to landing page from third party site then a visit is counted for the first time but if he comes again  during the same session, visit will not be counted. Hence visits are usually less than the number of instances.


Doesn't this sound similar to pageviews?  Instances are similar to page views in that they represent the number of "hits" that passed the given search engine, keyword, and/or referrer value into SiteCatalyst. Then why Omniture uses instance as a metric? Well, these sound similar but these are not same exactly same (mind it).

Here are some of the facts about instances:

• All the views for a page might not have come from the referrers and hence you can expect your referrer report to show less pageviews than the PageViews report
• In a Referrer report, for a given referral URL, an instance is counted when ever the page is viewed and referring url is passed to SiteCatalyst. The referrer persists untill the user moves to some other page. 
• Now an interesting fact is that if user clicks on back button on the second page to go to the landing page where he came from a referrer, then again an instance will be counted for referrer.
• Summary value in referrer type report might have more instances than detailed view because Sitecatalyst records only top 25,000 uniques referrers for each day for optimization purposes.

The most significant difference between instances and page views is that events other than page views like custom links, exit links, file downloads, media data, etc can pass referrer data (and therefore can record instances), but these non-page view events do not count page views. Thus it is possible, in some cases, for more instances to be reported than site-wide page views. Please note that this is not always true for all non page view events and is case specific.