ComScore's sampling problem

We have a few more details on ComScore Media Metrix’s recent restatement of their at-work measurements, thanks to the Internet Advertising Report.

First, ComScore acquired Media Metrix’s sample, but not its software. Second, ComScore was combining two samples collected by very different means (telephone and email recruitment), and combining two very different measuring systems (end-user and proxy server based) at the same time it was expanding its sample.

Without the tracking software, ComScore incorporated its own server-based measuring system with the November 2002 release of Media Metrix 2.0.

In addition to the 50,000 home Internet users recruited via Random Digital Dial sampling methodology, Media Metrix 2.0 expanded its measurement panel to 120,000, including 35,000 samples of at-work and university users.

No wonder there were some problems with their numbers.

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