This recent article from Online Information Review seems interesting in quantifying search success of Google vs some more open search tools, using a set of articles from ecology, economics and sociology.

From the Findings
“Of the 2,519 articles, 967 were found to have OA versions on the world wide web. Google and Google Scholar found 76.84 per cent of them. The results from OpenDOAR and OAIster were disappointing, but some improvements are noted.”

I think I was at least as interested in the % of items available OA as I was the success rates for the various search tools. The articles used in the study are mostly published between 2003-2005.

DAve C.