There are methods and apparatus, including computer program products, for providing a probability tree of nodes in which each node is associated with a tries value and a success value, and at least one node is associated with a computed probability value representative of a predicted response rate for an advertisement creative; and computing a first probability value for a first node of the probability tree based on its associated tries value and success value, and a computed probability value associated with a parent node to the first node. In one exemplary embodiment, the first probability is computed according to the following equation: Probability = ( 1 + Success node - Success Child ) ( tries node + 1 probability Parent - tries child