15. The one or more computer systems of claim 13 , wherein the smoothed browse node prediction uses a formula: P ⁡ ( Click x | Q ) = ∑ N ⁢ w x ⁢ Click x + α ∑ N ⁢ w x + α / P ⁡ ( Click x ) wherein P is a probability, a is a smoothing factor, Click x is an observation of a click in browse node x, N is a number of observations of query Q, w x is a weight for an impression, and P(Click x ) identifies a prior for clicks in browse node x.
13. The one or more computer systems of claim 11 , wherein the category is determined through a process, wherein the process includes one of the following: simple prediction, smoothed browse node prediction, expanded query group, N-Gram generative model, estimated probability as prior, or interpolation between multiple prediction models.