Quantitative and qualitative methods are based on contrasting assumptions and ideologies about social phenomena and knowledge. In order to avoid being accused of proposing a shotgun marriage, mixed methods research must address not only why mixed methods are needed in a study, but also address how these two approaches or methods can be meaningfully combined in a study while minimizing tensions and conflicts. In theory-driven evaluations, the application of mixed methods is justified and applied under a conceptual framework called program theory. The conceptual framework of program theory (Chen, 1990, 2005) provides a plan and agenda for mixed methods to work collaboratively and de-emphasizes their differences and incompatibilities.