Google announced on Thursday that they were changing the definition of a visit/session in Google Analytics – http://analytics.blogspot.com/2011/08/update-to-sessions-in-google-analytics.html. The key difference is that a new visit will be recorded whenever a visitor re-enters a website with different traffic source information. Previously, there had to be 30 min of inactivity before a new visit could commence. There is a second change with closing a browser no longer ending a session.
There was announced as a small change by Google with most users seeing less than a 1% change. That doesn’t tie in with the data I am seeing over a number of accounts and feedback from other sources where changes of 10%+ have occurred. This impact on data is most obvious in ratio metrics such as conversion rate, bounce rate and average time on site.
Which metrics are affected?
One thing to make clear is that the only absolute metric that should have changed is visits. There should be no impact on unique visitors, page views, conversions, time on site, etc. Any change here is due to different factors not relating to this change in the definition of a visit.
As visits have increased, any metric which is an absolute number divided by visits will have decreased. This can be seen in metrics such as page views per visit, conversion rates and average time on site.
It is a different situation for bounce rate. If a visitor has clicked through to a website on one traffic source, viewed a single page and then re-entered on a different traffic source, this is now counted as a bounce for that first traffic source. As such it is likely that the bounce rate will have increased for many websites.
Another metric with a unique impact is % New Visits. Any visitor who re-enters the website and creates a second visit will be treated as a Return Visit for that second visit. Therefore the % New Visits will decline.
What will the impact be on my metrics?
The scale of the change will vary from website to website. It depends on whether visitors will be re-entering the site from multiple traffic sources or not. Some websites will see no impact. A website which has visitors using Google or a 3rd party website (aggregators) as their internal search tool will likely see a big change as visitors are constantly re-entering the website.
I am not certain which traffic sources will be most affected by this. There was no clear trend in my admittedly brief investigations that I could see. The more cynical people out there are sure to suggest that Google Adwords will report a lot more traffic and conversions.
Can I still use Google Analytics data?
Let’s get to the key question, how much is this likely to impact your understanding of business performance and your ability to use Google Analytics data to improve performance? In the long term, not at all.
Neither definition of a visit is inaccurate; the numbers were correct previously and are correct now based on the definition at the time. It makes it difficult to compare week on week numbers right now but that won’t be a problem after a few weeks. After that, you should be looking at your current numbers when evaluating performance, the change will have no impact on your understanding of performance.
The biggest issue is for people who have just launched a new marketing campaign or website tool/feature. It is going to be very difficult for them to evaluate the impact of this launch. They are the big losers here. For everyone else, we are just going to have to grit our teeth and ride it out for a couple of weeks. Arguably there is even an opportunity here to get a better understanding of business performance by comparing data from the two definitions.
How do I check my numbers?
The change happened on the 11th Aug but it will hit your numbers at different times depending on your time zone. I recommend extracting data for key metrics at daily level and checking the week on week change. If your numbers are affected, you should see a step change occurring on either the 11th or 12th Aug which will continue for seven days before settling down.
Why has Google done this?
As to why Google has made this change, I think it is an attempt to make the web analytics data easier to understand, particularly for marketers. The definition of visits is simpler, every time someone enters the website, it is a visit. As mentioned in the announcement, it will align with data for multi channel funnels which was likely a key factor in this decision. So better for marketers and light users of web analytics, maybe not so good for experienced web analysts who disagree that this is the common definition of a visit.
Given the outcry we are already seeing, I can understand why this was not announced in advance or available for testing. It is a change that Google wanted to make, they knew there would be some unhappy people out there and so just made this a quick rather than drawn out process.
This is going to be very annoying for a few weeks and then shouldn’t matter. There will be some difficult discussions with senior management over why/how the numbers have changed and getting them to understand that this doesn’t mean the website is performing any differently. To make these discussions easier, I recommend using unique visitors and even page views as a measure of traffic for the next couple of weeks until you have a clear view of the data.
As someone has said in the comments on the announcement, make sure you annotate your GA accounts with the date of this change. If Google wants to make everyone’s life a bit easier, they could push out a global annotation stating this.