In the online world, there is this relentless obsession with relevance. Everything has to be relevant, relevant, relevant. The way the word is normally translated in common speech is that something is relevant when you're interested in it at a particular time and place. Facebook's news feed is all about showing you things that are relevant to you from your friends. Google wants to show you the most relevant pages for a given search. And, to my mind, they actually do a pretty good job doing these things.

As businesses, though, what they really want to do is serve up the most relevant advertisements. That is to say, they want to serve up the ads that you're most likely to click on. So they refine and refine and refine the algorithms they've got with more and more and more data in the quest to find ads that people want to click on.

It's fair to ask, I think, how are they doing? One indication comes courtesy of this infographic that these marketers created showing the differences between Facebook and Google's ad networks. It contains three remarkable stats about clickthrough rate (CTR), which is the percentage of the time a user clicks on an online advertisement. The average, these marketers say, is about 0.1 percent. Facebook's CTR is below average at 0.051 percent and Google's is above average 0.4 percent.

While these differences are meaningful and say something powerful about Google and Facebook, let's do the math on those percentages to see how relevant the ads you're seeing really are. For Google, people are clicking on about 1 of every 250 ads they see while searching. For the average, it's 1 out of every 1,000 ads. And for Facebook, people are only clicking once every 1,961 ads they see.

That's the reality of relevance in the online world -- and, not so incidentally, while companies are so eager to scoop up any data they can to increase the likelihood that you'll click.