It appears that in December 2009, the 112 of the comScore top 1000 sites that were entirely or partially measured by comScore’s hybrid methodology saw on average a 30% increase in unique visitor counts. Some of the largest discrepancies appear to show up with sites that tend to get more traffic from areas where the [...]

comScore (ah the joys of weird capitalization!) is acknowledging that its panel-only approach to measuring user traffic may not be as good as they have previously said, and responding somewhat to the incursion of Google and Quantcast into their reporting and measurement territory by incorporating site-side measurement into their figures. As Peter Kafka points out [...]