Policy impact assessments, or simply impact assessments (IAs), are formal, evidence-based procedures that assess prospective economic, social, and environmental effects of a public policy proposal. 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. 
Key types of impact assessments include global assessments (global level), policy impact assessment (policy level), strategic environmental assessment (programme and plan level), and environmental impact assessment (project level). Impact assessments can focus on specific themes, such as social impact assessments and gender impact assessments.
IAs can improve legislation by:
Procedure.
The department which is responsible for the policy proposal usually has to carry out the IA. Although the purpose and orientation of IA procedures differ, IA guidelines in the various jurisdictions all follow a similar set of steps to be followed by desk officers:
The analytical steps, which mainly relate to step 2, can be set out as
i. Problem definition
ii. Definition of policy objectives
iii. Development of policy options
iv. Analysis of impacts
v. Comparison of policy options and recommendation of one option
vi. Defining monitoring measures.
Methods.
Throughout the IA process, methods can be used for support. In recent years governments have increasingly invested in developing and applying methods and tools for IA.
Depending on usage, IA methods can be classified as methods for
References.
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