Could the intro of the cookie message affected traffic this much?

Traffic dropped off a cliff following the intro of the cookie message

[jonnyruss]

I'm analyzing the traffic of a prospective clients site. The traffic dropped off the cliff towards the end of May 2012 as they introduced a pretty strongly worded cookie message on their site following the EU cookie ruling.

My question is could the cookie message really have caused the huge drop in traffic (around 80% down) ever since its introduction or is it likely another cause?

Thank you in advance.

[lucy24]

You need a little more information. The most fundamental question is: 80% in number of unique visits, or in number of pages requested?

The sequence goes:

--visitor requests a page
--site shows Cookie message
--visitor says "Yeah, yeah, I understand, show me the ### page already"
--site makes additional cookie saying "visitor has agreed to accept cookies" (this line is a guess on my part, because otherwise you'd have to show the same message on every single page)
--site serves page
--site serves additional pages as requested (again, this is where I'm guessing that there are no further Accept-cookie messages)

At what point in the sequence is the drop happening? Are users declining to follow through on their initial request, or are they visiting the first page but not continuing to additional pages?

[jimbeetle]

Have you checked to see if the drop coincides with any SE algorithm or data updates?

[MartinBrown]

I wonder if the cookie message affected Google/Bing bots reading the site. Is the site still OK within the SERPS?

[phranque]

welcome to WebmasterWorld, jonnyruss and MartinBrown!

I was going to ask the same question as MB.
have you checked the cached version of your page(s) in google or tried "fetch as googlebot" in GWT?