The theory of stochastic processes deals with systems that develop over time in accordance with probabilistic laws. The basic concepts involved in two types of continuous-time processes are the idea of a constant probability of occurrence in the point event process and the extensions necessary for the discrete state process. The required mathematical skills and technical literature in this are discussed. It is recommended that researchers responsible for collecting longitudinal data change their method from a reference point to an event history approach to item construction. The difference between the two approaches is illustrated with sample questions from two longitudinal studies sponsored by the National Center for Education Statistics. (Author/PN)