5. The method of claim 1 wherein each impression in the plurality of candidate impressions comprises a message and an associated creative, the creative being a design of how the message is to be presented to the end-user.
5. The method of claim 1 wherein each impression in the plurality of candidate impressions comprises a message and an associated creative, the creative being a design of how the message is to be presented to the end-user. 6. The method of claim 5 wherein the plurality of candidate impressions comprise: a first message with an associated first creative; the first message with an associated second creative; and the first message with an associated third creative; wherein the first, second, and third creatives are different from each other.