The numbers of users reported by Facebook, Twitter, Google, and many other sites, are closely watched. They reveal trends in adoption and they are one of the few public metrics available to analysts trying to assign value to companies preparing an initial public offering.

But how accurate are these numbers?

In some anecdotal cases, the number of users, active and actual, could be as small as one-third. And nearly one-half of user accounts could be fake or contain no user profiles.

No user profiles means very little usable data for marketing or advertising campaigns. This is a huge hole in social media platforms.

It means corporate marketers and advertisers will not be able to reach and engage with the numbers they expect, resulting in increased costs and a discouraging ROI.

If corporations aren’t able to use social media to reach large numbers of consumers, the value of platforms such as Facebook will be severely diminished.

How large is this problem of fake and empty user profiles?

Here is an analysis performed by Kevin Kelly, a former editor of Wired magazine and a book author, on 560,000 people that have him in their G+ “circles.”

World map of Flickr and Twitter locations

Red dots are locations of Flickr pictures. Blue dots are locations of Twitter tweets. White dots are locations that have been posted to both.