William Bunker Hansen (born November 15, 1949) is a researcher in the field of prevention science.

His program development approach focuses on longitudinal statistical mediators and devising strategies for altering normal developmental processes.

[6][7] He is currently directing the development of Virtual Controls,[8] a strategy to evaluate disseminated prevention programs when randomization is not possible and recruitment of comparison sites is challenging[9][10] Hansen was among the first drug prevention researchers to acknowledge that quality of implementation (often referred to as fidelity) was a key moderator of the success of intervention efforts.

Fidelity assessment tools have been built into Evaluation Lizard and Virtual Controls as an option available to users.

While this has not been a primary focus of his research, he has nonetheless published several empirical studies that have directly influenced the development of the prevention programs.