[1] They have been incorporated into policy making in the OECD countries and the European Commission.
If the assessment is favourable, and the proposed policy is enacted—after a suitable length of time for the policy to gain traction—it might be followed by an impact evaluation; ideally, assessed impacts before the fact and evaluated impacts after the fact are not wildly divergent.
In some cases, impact becomes politicized due to a change in the governing regime between assessment and evaluation, and non-congruence might be amplified for ideological reasons.
In other cases, the world is a complex place, and assessment is not a perfect art.
In recent years governments have increasingly invested in developing and applying methods and tools for IA.