dummy or reference it?

Strong evidence from survey research consistently shows that heavy viewers of violence on television are more likely to engage in aggressive behavior than are light viewers. Moreover, viewers of violent television express more willingness to use violence to resolve real interpersonal conflicts. However, these correlational studies simply say that television violence viewing is associated with holding favorable attitudes toward the use of violence and aggressive behavior. Such studies alone are not sufficient evidence that media violence causes aggression. Furthermore, correlational evidence does not provide evidence of the direction of the causal relationship. It might be that people inclined to act violently are more likely to watch television violence, and so it is their predisposition toward violence that leads to viewing violent TV, and not the other way around.

Q) Does "it" refer to something in the previous sentence? Or is "it" just dummy it?