1. A method of predicting outcomes of marketing campaigns comprising more than one campaign step, by a computer system, the method comprising: defining, by the computer system, a marketing campaign as including at least first and second campaign steps, the second campaign step configured to be performed after the first campaign step and only toward customers who responded to the first campaign step; compiling first customer objects in a repository, the first customer objects corresponding to a first target group of customers registered in the computer system, at least one constraint taken into account when compiling the customer objects; predicting, by the computer system and the first customer objects, a number of responses to be received if the first campaign step were performed toward a first target group of customers, each customer having a response probability; compiling, by the computer system, second customer objects from the first customer objects, the second customer objects corresponding to a second target group selected from the first target group using respective response probabilities of individual customers in the first target group, the second target group being a subset of the first target group and substantially equal to the predicted number of responses; predicting, by the computer system and the second customer objects, an outcome of performing the second campaign step toward the second target group; and generating, by the computer system, a prediction for the marketing campaign using at least the predictions regarding the first and second campaign steps.