APA Dictionary of Psychology

inability of a researcher to document the results of a study when all participants have reached a target event (e.g., achieving a specific milestone) at the conclusion of the study period. This may occur for one of three reasons: A participant may never experience the target event or may experience it after the observation period has ended; a participant may experience a competing event that prevents them from experiencing the target event; or a participant may be lost to attrition. Compare left censoring.