Google Analytics update may have a greater impact than expected
Last week Google rolled out a minor but significant change in the way user sessions are calculated. They weren’t expecting many sites to see much of a change in their metrics, but a number of sources in the analytics community are reporting significant shifts, most likely caused by the algorithm change.
The changes only apply to visitors who leave a site, then re-enter by other means within the space of half an hour, or when a user closes their browser for a short time, then re-opens it. Under the old regime closure of the browser meant closure of a session, and that is no longer guaranteed. On the other hand, arriving on a site through organic search, bookmarking it, leaving and returning within 30 minutes would not have counted as two separate sessions before the changes came through, but it will now.
Sound complicated? It’s not the exact definition of a session that most users need to worry about, but the change in definition. Whenever a metric is altered, it can mean confusion. Some figures may go up and some may go down, even though there is no change in traffic pattern.
Google didn’t think that this batch of modifications would have much of an impact (and there were good reasons to tweak session definitions) but many reliable sources are seeing swings of up to 10% or more when comparing figures from before and after the algorithm change.
Conversion rates and average time on site measures are most likely to be affected, along with total visitor numbers and any metric calculated using it.
When tracking the changes in your Google Analytics metrics from July to August, be aware that you might see the effect of the tweak. If you want to check, take a close look at the data on either side of the 11th/12th of this month. Any sudden, statistically unusual jumps that can’t be otherwise attributed could be down to this GA update.