In the context of search models, the process by which participants leave or stop searching.
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Description
In models of search — situations where an agent looks through options until it decides to stop — mortality is the process by which participants leave the pool of active searchers. A participant can exit because a satisfactory option was found, because the search was abandoned, or because the participant is no longer available to continue. Mortality matters because it changes who remains in the search: if the participants most likely to succeed leave early, the remaining pool looks different from the original one, and any conclusion drawn from it can be misleading. This kind of exit process is central to interpreting data from job searches, mate selection, online marketplaces, and any setting where the population being observed shrinks over time.
How it works
Each participant in a search model faces a chance of leaving at every step, and that chance usually depends on how good the options encountered so far have been. A searcher who finds an acceptable match exits immediately; a searcher who finds nothing acceptable may keep going or give up after some time. Because exits are selective — they happen more often for some kinds of participants than others — the composition of the surviving group drifts as the search proceeds. Analysts therefore model both the search behavior and the exit behavior together, since ignoring mortality produces biased estimates of how long searches last and how successful they are.
In practice
Search-and-exit models are used in labor economics to study unemployment durations, in online platforms to analyze user churn, and in epidemiology to track how a population at risk shrinks over time.
Every one of us has wondered at least once how many years we'll live. In 1996, nearly two and a half thousand Japanese people over sixty answered that question in a national survey. Their answers became a kind of mirror reflecting hopes, fears, and habits of thought. Twenty-eight years later, researchers compared those forecasts with actual dates of death and found that the mirror was warped, but not useless.