Attribution is the next big thing in web analytic. Currently, no tools offer the possibility (out of the box) to customize attribution measuring.
Attribution is the feature that make possible to know which channel (SEO, PPC, Campaign, etc) contribute to the conversion. For example, Bob click on our banner and visit our web site, he take a look around and leave. Two days later, Bob did a search on Google with our brand term and visit on website again. After awhile he leave. The next day we come back to our website (he remember the url) and convert. Without attribution, we would have to give credit to this conversions to direct traffic. But with last-click model, we gonna give credit to Google (we ignore direct traffic in attribution). Using a first-click model, we gonna give credit to the banner. With all model, we gonna give credit to banner and Google. And finally, with even-model, we give half credit to the banner and the other half to Google.
In almost all tools, the default model is: last-click. For the moment, only Coremetrics give you a choice of different attribution models: last-click, first-click, even, all and custom. (The other tools, like Omniture, are capable of doing so too, but this is view as custom reports.)
But why have to choose? I would like a tools capable of giving access to all the attribution model without having to choose one over they other.
I play a little with Piwik, and it seem only same session attribution is available for the moment. And I didn’t see in the milestone and upcoming version anything about multiple sessions attribution model. I believe this is something to take in account during the earlier phase of the project so the database structure would support this someday.
(Google Analytics offert a 60 days last-click attribution models.)