Evidence-based policy can help improve and continue successful policies, while finding negative or unintended consequences can point to areas for improvement. But evidence-based policy comes at a price. Rigorous evaluations take time, and they require input of human resources and data. Not least, evaluations require good communication on how to interpret findings and how to put them into perspective.
These costs of evaluations can be reduced by setting up the right infrastructures: Legal mandates and administrative procedures: There will be a natural tendency of policy evaluations to be in a time and resource conflict with other administrative tasks. Moreover, unless clear procedures for evaluations have been established, political considerations may dominate the administrative agenda.