A study from search analysis firm Compete – posted at marketing website Seeking Alpha – says that there were 500 billion fewer searches performed in November of 2009 than in the previous month.

Nearly all of the top search engines lost volume, according to Compete, which may have affected search engine optimization (SEO) efforts for the month of November. November saw 12.5 billion total search queries, but Compete’s analysts said that the loss of volume masked some encouraging signs for the search market.

Yahoo, surprisingly, was the clear winner in the month of November, gaining half a percentage point of market share and leading the pack with a 1.3 percent increase in sponsored clicks. Despite the downturns, all three of the major search engines posted increases in sponsored clicks – Compete speculates that this is due to holiday marketing – and referrals.

As previously reported by Brafton, this points out a number of problems with using rankings as a primary metric for search engine optimization (SEO) success, in that the rankings would not indicate an overall search downturn.