Also see…

Nielsen Note: Effective with October 2007 reporting, Nielsen Online has made several enhancements to its MegaPanel service. These enhancements include more granular reporting, increased accuracy, an expanded Internet universe and more advanced tracking. Because of these methodology changes, however, pre-Oct. ‘07 results from MegaPanel-based products, including MegaView Search and MegaView Online Retail, cannot be trended with more recent results.