A correction has been made in this story. See below for details.

How big is big? The two bars represent the share of the revenue generated by the world's 50 largest agency companies. The bar on the left is the Big Four holding companies: WPP, Omnicom Group, Publicis Groupe and Interpublic Group of Cos. The bar on the right, noticeably smaller, is the next 46 companies. That's big.

How big is biggest? WPP alone has revenue greater than agencies 8 through 50.

And yet big is getting ever so smaller. In 2010, the four largest holding companies made up 65.4% of the total revenue of the top 50. That's actually been creeping downward from 69.4% in 2006. But still, big.

But if you want to get into a little more detail, Ad Age's new 2011 Agency Report digs into the Big Four and the rest to give you an incredibly comprehensive look at how nearly 1,000 agencies stack up -- including un-rolling the holding companies and networks.

For more stats, follow @adagestat on Twitter.

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CORRECTION: In an earlier version of this post we incorrectly stated that the revenue for agencies 5-50 (the "next 46") was $35.2 billion. We erroneously double-counted Publicis Groupe and Interpublic Group of Cos. The numbers are actually even further apart. The revenue for the top four are nearly double the rest of the top 50. This was brought to our attention in the comments below. Reader Chris Mulligan also took issue with our graphic presentation, which has now been changed to display the corrected figures as fairly as possible. We welcome the feedback and we will present copies of our birth certificates upon request.