We have seen in the last chapter that a set of processing rules and a set of input probabilities imply a rather large set of features of the populations produced by simulation. Some features, like size, are unpredictable, but others, including the age distribution, proportions married, difference in age between spouses and between parents and children, even such a nonobvious feature as the variance in the male age-specific fertility schedule, are predictable within narrow ranges because they are produced—however complex and indirect the pathway—by the input probabilities and the rules of simulation.