Google announced on Google+ a new AdWords tool for determining the attributions that lead to your conversion. The tool is named the Search Funnels Attribution Modeling Tool.

The Search Funnels Attribution Modeling Tool offers five models for assigning value to the keywords, ad groups, and campaigns that lead to conversions. While most advertisers assign the last click to the conversion, that might not be a true value.

The attribution models included in the Search Funnels Attribution Modeling Tool are:

Last Click model Last click: Gives all credit for the conversion to the last-clicked keyword
First Click model icon First click: Gives all credit for the conversion to the first-clicked keyword
Linear model icon Linear: Distributes the credit for the conversion equally across all clicks on the path
Time Decay model icon Time decay: Gives more credit to clicks that happened closer in time to the conversion
Position Based model icon Position-based: Gives 40% of credit to both the first- and last-clicked keyword, with the remaining 20% spread out across the other clicks on the path

AdWords said on Google+:

More details over here.

Forum discussion at Google+.