My article on how the “Yellow Pages Usage Stats Are Likely Wrong ” went up earlier at Search Engine Land, and the details I highlight in it provide some strong circumstantial evidence that this year’s earlier industry statistics stating that print YP book usage hadn’t dropped over the year previous are likely incorrect.
As I point out, those statistics were all based on telephone polling, and those polls missed having representative samples of cell phone only households, according to their published methodology. Various research groups and government agencies have been saying that this is a significant chunk of the population — anywhere from 13.6%, growing to as much as 25% by the end of this year.
When you further realize that this segment is younger, and likely earlier adopters of technology, you can see that there might be a strong reason to believe that their usage profiles probably differ significantly from the land-lined population — they’re probably using print YP less than those who were polled.
This chain of reasoning is an assumption — there’s no absolute evidence to support it. But, the lack of representative sampling in the original polling data leaves us with no alternative but to try to put the findings up against logical reasoning.
It’s hard to monitor and assess usage of offline media, so print yellow pages are not the only ones that struggle sometimes to show value proposition. Print newspapers, magazines, billboards, and others also have similar difficulties in showing how many consumers see them.
Of course, some people have pushed real hard to count offline media — Google has apparently been interested in this Eyebox device  which counts when people look at wall ads or billboards.