Credible research on CT to page 2, 3, etc?

[ShooflyPie]

Can anyone share some citations for research about how often searchers click through to page 2 or 3 of search results? I've seen people blithely throwing around numbers, but they never seem to footnote where they get their data from.

I'm aware that it may vary from search engine to search engine, and it probably varies based on the query, too. But even incomplete data would be better than none, right?

Thanks in advance!