Neglected challenges to evidence-based policy-making: the problem of policy accumulation

Claims for evidence-based policy-making are motivated by the assumption that if practitioners and scholars want to learn about effective policy design, they also can. This paper argues that this is becoming more and more challenging with the conventional approaches due to the accumulation of national policy portfolios, characterized by (a) a growing number of different policy targets and instruments, that (b) are often interdependent and (c) reformed in an uncontrolled way. These factors undermine our ability to accurately relate outcome changes to individual components within the respective policy mix. Therefore, policy accumulation becomes an additional source of the well-known ‘attribution problem’ in evaluation research. We argue that policy accumulation poses fundamental challenges to existing approaches of evidence-based policy-making. Moreover, these challenges are very likely to create a trade-off between the need for increasing methodological sophistication on one side, and the decreasing political impact of more fine-grained and conditional findings of evaluation results on the other.