Not sure how applicable these results are to medical search….

“The study found that 62 percent of search users click on a link within the first results’ page, up from 60 percent in 2004 and 48 percent four years ago. Additionally, nearly all searchers–90 percent–click on a link within the first three pages, up from 87 percent two years ago and 81 percent in 2002.”

“When researchers asked users at what point they either revised their queries or moved to another search engine, 16 percent replied that they did so after reviewing the first few entries, and 25 percent said after the first page. An additional 27 percent changed either their queries or search engines after the first two pages, while 20 percent did so after three pages; just 12 percent stayed with the search terms and/or engine beyond three pages.”

See here for more details.