To solve the second problem (of inadequacy of binary classification algorithms), we require learning algorithms not only to classify, but also to classify with a confidence measurement, such as a probability estimation or certainty factor. This allows us to rank training and testing examples. The ranking of non-buyers (from most likely to least likely buyers) makes it possible to choose any number of likely buyers for the promotion. It also provides a fine distinction among chosen customers to apply different means of promotion. Therefore, we need learning algorithms that can also produce probability estimation or certainty factors. We will discuss such algorithms that we used in Section 5.1.