Disagreements about the hypodermic needle theory may be based on how audiences are classified. For example, the pro-hypodermic perspective suggests that despite differing types of audiences, the theory remains valid if a direct effect occurs. However, many anti-hypodermic views instead note that the theory can only be applied if the effect works on a similar, mass group of people. Other interpretation differences depend on whether researchers involve mediating and intervening variables in case studies. This may include the influence of an audience’s prior knowledge and background.