Changes in key variables that are introduced in a systematic way to allow for an examination of the effects that one variable has on another. For example, a firm could charge different prices in different geographical regions to assess price role-playing case to 15 groups of health-care executives; only one group proposed an experiment, and this group was successful at implementing change while all other groups failed. Finally, Armstrong gave 14 groups instructions on how to propose experiments in this situation; of these, 12 were successful at gaining acceptance in role-playing exercises.