According to some theories of recognition memory (e.g., S. Dennis & M. S. Humphreys, 2001), the number of different contexts in which words appear determines how memorable individual occurences of words will be: A word that occurs in a small number of different contexts should be better recognized than a word that appears in a larger number of different contexts. To empirically test this prediction, a normative measure is developed, referred to here as context variability, that estimates the number of different contexts in which words appear in everyday life. These findings confirm the prediction that words low in context variability are better recognized (on average) than words that are high in context variability.In a typical recognition memory experiment, a list of words is studied, and memory is tested subsequently by showing subjects both words that were studied (i.e., targets) and words that were not studied (i.e., foils). The subject's task is to discriminate the targets from the foils. Of course, subjects have encountered words a large number of times in many different contexts prior to the experiment. Hence, the subject's rather daunting task is to discriminate the most recent encounter with a word from all prior encounters.Theories of memory usually address this issue by making a distinction between item and context information (e.g., Anderson & Bower, 1972;Dennis & Humphreys, 2001;Humphreys, Bain, & Pike, 1989;Jacoby, 1991;Maddox & Estes, 1997;McGeoch, 1942;Mensink & Raaijmakers, 1988;Raaijmakers & Shiffrin, 1981;Shiffrin & Steyvers, 1997): Item information represents a studied stimulus (e.g., a word), and context information represents the environment in which the stimulus was encountered. According to these theories, when an item is studied, both item and context information are stored in an episodic trace, and when recognition memory is tested, memory is probed with a retrieval cue consisting of both item and context information. The critical role context plays in the retrieval cue is to restrict the probe to the relevant subset of memory traces (as defined by the task). Those episodic traces that contain context information similar to the retrieval cue might become members of the "activated" subset of memory and contribute information to the recognition decision. Hence, the to-be-remembered encounter with a word can, in principle, be isolated from prior encounters according to the similarity between the context used in the retrieval cue and context information stored in memory.