Performance tests are used in training evaluation to (1) certify student achievement, and (2) diagnose weaknesses in the instructional system. Proficiency measures that focus on task outcomes (product) normally provide data relevant to the first purpose, whereas measures of how the tasks are carried out (process) pertain to the second. Time or cost factors sometimes preclude the use of product measures, leaving measures of task process as the only available criteria for evaluating training outcomes. Instances in which process measures are typically substituted for product measures are described in this paper with reference to the types of tasks for which the substitution is valid and those for which it is invalid. Theoretical and practical issues pertaining to the use and misuse of process measures are discussed. (Author)