While all of us fight to get Google Analytics referral spam under control, one piece of well-intentioned, but bad advice comes up over and over again: use the Referral Exclusion List. Some people (myself included) have stated that is a bad idea, but no one has taken the time to really explain why. Here is the Why…
[if you want to know what you should do, read the Definitive Guide to Removing Referral Spam]
According to Google, the Referral Exclusion List is intended to be used “to exclude traffic from a third-party shopping cart to prevent customers from being counted in new session and as a referral when they return to your order confirmation page after checking out on the third-party site” *.
But people get confused by the phrase:
“When you exclude a referral source, traffic that arrives to your site from the excluded domain doesn’t trigger a new session.”
So people assume that means it will exclude the visit from being reported. What is actually happening is that Google is trying to connect the return visit to the original visit, and it prevents the referral information from being recognized. There is still a visit, it just comes from nowhere (i.e. direct).
Let me demonstrate…there is a link on stackoverflow.com to one of my (lonely) websites. If I click on the link, it appears in Google Analytics as a referral from stackoverflow:
If I then add stackoverflow.com to my Referral Exclusion List:
And click that same link from a different browser (which means it is a new user as far as Google Analytics knows), you can see Google Analytics still records the visit, but since the referral information has been stripped off, it is seen as a Direct visit.
Adding a lot of spam domains to your Referral Exclusion List can cause those spam visits to be registered as Direct traffic. Sure the spammy referrals are gone, but your metrics are still messed up!
Bottom line: Do NOT use the Referral Exclusion List for cleaning spam referrals.