• by Laurie Sullivan , Staff Writer @lauriesullivan, July 31, 2009

A comScore study of Yahoo and Doubleclick cookies done several years ago revealed 30% of Internet users delete cookies in a month. A recent study suggests rates are up 10%. They delete five different cookies for the same site in a month on one computer, according to Gian Fulgoni, chairman and co-founder at comScore,

Fulgoni told attendees during the opening remarks at the OMMA Metrics & Measurement conference in San Francisco on Friday that cookie deletion creates major problems in determining ROI for campaigns. It creates 2.5 times overstatement of unique visitors in a server log, depending on frequency of site visitation, as well as up to 2.5 times overstatement of reach and a similar understatement in frequency in ad server logs.