As the chapters in this volume illustrate, an important class of questions arising in life-course research ask “whether” and, if so, “when” a variety of events occur. Researchers investigating the consequences of childhood traumas on later well-being, for instance, ask whether an individual ever experiences depression and, if so, when onset first occurs (see Chapter 3). Other researchers ask questions about whether and when street children return to their homes (Chapter 4), whether and when high school dropouts find work (Chapter 5), whether and when high school graduates enroll in college, get married, and begin a family (Chapter 10), and whether and when young children make the transition between adult-supervised care and self-care (Chapter 8).

Familiar statistical techniques, such as regression and analysis of variance, and their more sophisticated cousins, such as structural equation modeling, are ill-suited for addressing questions about the timing and occurrence of events. These usually versatile methods fail because they are unable to handle situations in which the value of the outcome – whether and when the event occurs – is unknown for some people under study. When studying event occurrence, this type of information shortfall is inevitable. No matter how long a researcher collects data, some people in the sample will not experience the target event while under observation; some adults will not have a depressive episode, some street children will not return to their homes, some high school graduates will not marry, and some young children will not be left alone unsupervised.