A sales prediction system predicts sales from online public discussions. The system utilizes manually or automatically formulated predicates to capture subsets of postings in online public discussions. The system predicts spikes in sales rank based on online chatter. The system comprises automated algorithms that predict spikes in sales rank given a time series of counts of online discussions such as blog postings. The system utilizes a stateless model of customer behavior based on a series of states of excitation that are increasingly likely to lead to a purchase decision. The stateless model of customer behavior yields a predictor of sales rank spikes that is significantly more accurate than conventional techniques operating on sales rank data alone.