Yahoo said it would migrate its U.S. search advertisers to its new ranking system on Feb. 5.

The transition is a critical bet for Yahoo, which has fallen behind Google in the booming search marketing space.

The key change for advertisers will be the new ranking methodology. Under its current system, advertisers bidding the highest for terms are listed first when those words are searched. Its new platform takes a cue from Google by basing rank on a combination of the click price bid and its click rate, both past and expected. This means an ad with a lower bid price but higher click rate could rank higher.

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