1. A computer-readable storage device storing computer-executable instructions for controlling a computing system to generate a classifier for predicting travel item prices, the computer-executable instructions implementing a method comprising: providing travel information for travel items on various observation dates; generating a feature vector for each travel item for each observation date based on the provided travel information; assigning a label to each travel item for each observation date with enough subsequent observation dates to generate a label indicating what the price direction prediction should have been for the travel item on the observation date, the label for each travel item for each observation date being derived from the provided travel information for that travel from subsequent observation dates; and training a classifier to make price predictions for travel items using the feature vectors and their labels as training data.