Explained: Sources in Google analytics

Looking at various related blog posts, I’ve realised many people don’t fully understand or fully explain how traffic sources are attributed in Google Analytics.

A Cooked named ___utmz

Let’s get straight to the details about sources…

  • Uses a cookie called ___utmz
  • Only gets updated each time the source is different to the source stored in the cookie (excluding direct visits)
  • The utmz cookie lives for 60 days since it was last updated

If you want a full run down then Analytics Market give an excellent and detailed explanation of all the Google Analytics cookies on their blog.

Detail of a screenshot from Google Analytics

All this means that if a visitor reaches your site (irrespective of landing page) via Google, then that visitor (note visitor not visit or page view) will have Google attributed as the source for every page they look at across every visit they make to your site. This will be the case until 60 days have past or the very same visitor comes in from another source (such as a link in a newsletter, or by clicking on a banner, or on an adwords ad)

Understanding Google Analytics reports

Make sense so far? The next part is to understand how this affects the way you read various reports in Google Analytics. Take the Top content report for example. Say your top page has had 5000 page views during the past month. Segment those by Source and perhaps 3000 of them are attributed to Google.

The easy conclusion to make is that those 3000 page views are directly attributable to Google; that an organic search in Google for a particular phrase led to the visitor clicking on a particular search result and visited that page on your site. In old-school log-file-based analytics, then yes, that would be the case (substituting Source for referrer).

Detail of a screenshot from Google Analytics

In Google Analytics the real explanation is that 3000 of the page views were displayed to visitors who had, at some point during the previous 60 days, arrived at your site after searching for something in Google and, if they made any repeat visits, then all of those repeat visits were direct.

Over-estimating the importance of Google

What this means is that unless your traffic consists of one-time-visitors and nothing else there’s a good chance you’re been over-estimating the importance of Google searches in generating page views. Unless you alter the default setting of the campaign cookie from 60 days to 0, then (apart from new visitors visiting once in the view time period) you can’t correlate page views/visits with their actual sources.

Understanding per-visit behaviour

Whilst I understand the usefulness of attributing sources for all subsequent direct visits for conversation analysis and goal tracking (it’s useful to know which initial source ultimately led to the conversation) it’s of much less use in understanding the per visit (and thereby more complete) behaviour of your visitors.