How big an impact do cookie deletion and multiple machine use have?

The impact of cookie deletion and multiple machine use/people use per machine is not uniform and differs significantly between sites. In some cases, though, it is not unusual to see an average of two (or more) cookies for every browser over the course of a month. A variety of factors must be taken into to account to properly adjust property level translations from cookies, to people. Quantcast has issued a Cookie Corrected Audience White Paper that discusses many of the considerations we factor into our model. At a high level, these include time period of evaluation, frequency of visit of user, cookie deletion rate and machine use behavior of a specific properties audience.