There was a debate some months back on the Yahoo Web Analytics Forum about “Authenticated User IDs vs. Unique Visitors” – which I somehow participated in with the post: Visits vs. Unique Visitors vs. Authenticated Users. Here I momentarily touch the subject of why cookie’s affect unique visitors, but not really any conclusion or take on my attitude on the metric as a whole.

I think we can all agree on the definition of a “Unique Visitor” being:

“The number of inferred individual people (filtered for spiders and robots), within a designated reporting timeframe, with activity consisting of one or more visits to a site. Each individual is counted only once in the unique visitor measure for the reporting period”

I also think we can agree that the deletion of cookies, whether 1st party or 3rd party, will cause the unique visitors metric to be inflated (comparing that to the actual number of people visiting your web property). We, the Web Analytics Industry, do know for a fact that this cookie deletion affect the measurement of the Unique Visitors metric. So:

Facts are:

• It’s important for clients to fully understand that this is an industry wide challenge that goes beyond just the Web Analytics industry. It is an Online Marketing challenge affecting Testing, Ad-Serving, Campaign Management, Behavioural targeting and other services who want to identity users.
• It’s also important to understand that it is not only the online marketing service industry that is affected – but the actual clients themselves, with all their needs for registering users and having them logged in on their web properties.
• The challenge is not new and we and the industry have talked about this for years – so one should not be shocked by the any such news.
• The Visit metric is still valid and many industry alumni (like Matt Belkin from Omniture) have talked about using this above “Unique visitors” for a long time.
• The Member ID metric is still valid and probably more important than ever – making sure clients deploy this should be pushed more from the industry.
• The inflated “Unique Visitor” metric is highly region and site specific and the stated fact about unique visitors are likely to be exaggerating the size of the site’s audience by a factor as high as 2.5, or an overstatement of 150% should be taken with a grain of salt.
• Finally one should know that a competing business to “cookie tracking” (the business we are in as WA vendors) is “panel based tracking” (the business comScore is in – this not saying their studies are not valid, just that it should be looked at carefully and probably not pushed as frightening as it is.

My take is:

• Focus more on the visit metric when possible
• As always - accept the fact that the numbers might not be 100% accurate and focus more on trends
• Create some kind of baseline for your own web property that can be used when looking at Unique- and Returning Visitors Metrics (remember this also impacts campaign management and the ability to attribute to a Original Source, which then affects CPA and so on).

I would like to drive your attention to the definition by the Web Analytics Association Web Analytics “Big Three” Definitions - by Jason Burby.