The task-switching literature routinely conflates different operational definitions of switch cost, its predominant behavioral measure. This article is an attempt to draw attention to differences between the two most common definitions, alternating-runs switch cost (ARS) and explicit-cuing switch cost (ECS). ARS appears to include both the costs of switching tasks and the switch-independent costs specific to the first trial of a run, with the implication that it should generally be larger than

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... CS, but worse is that the alternating-runs procedure does not allow these costs to be separated. New data are presented to make these issues concrete, existing data are surveyed for evidence that ARS is larger than ECS, and implications of conflating these measures are examined for existing theoretical constructs.