Journal article: When policymakers and private agents use models, the economists who design the model have an incentive to alter it in order to influence outcomes in a fashion consistent with their own preferences. I discuss some consequences of the existence of such ideological bias. In particular, I analyze the role of measurement infrastructures such as national statistical institutes, the extent to which intellectual competition between different schools of thought may lead to polarization of views over some parameters and at the same time to consensus over other parameters, and finally how the attempt to preserve influence can lead to degenerative research programs.