Turning impression logs into people counts turns out to be a pretty difficult problem. Even with cookies it's still very complicated. Facebook has publicly ac

Turning impression logs into people counts turns out to be a pretty difficult problem. Even with cookies it's still very complicated. Facebook has publicly acknowledged screwing it up several times. We could go back to the days of talking about "hits" on a website, but for most things where you'd care about these types of metrics, it's a pretty crap metric.