There is increasing support for evidence-based policy making [1] [2], which is based on the use of scientific methods.

The reasons for not basing policy on the available evidence are

• lack of awareness
  
• unsubstantiated beliefs
  
• being swayed by self-interest
  
• succumbing to outside pressure, and
  
• lacking the necessary skills
  

or in blunt terms

• ignorance
  
• prejudice
  
• greed
  
• corruption, and
  
• incompetence
  

An evidence-based policy seems likely to be a better policy for the public than any of these alternatives.

In my view policies should include

• aims (together with their relative importance if more than one), and the justification for them, including reasons for non-inclusion of other potential aims,
  
• methods to achieve those aims, together with the reasons why it is felt that those methods will work such as evidence of their effectiveness previously,
  
• reference to and comparison with comparable policies.
  

There should be a recognition that any first version of a strategy will contain flaws, and a desire that these flaws will be removed as far as possible via a process of consultation (analogous to peer review prior to publication in scientific journals). There are Government guidelines on consultation [3].

When drawing up an evidence-based policy, if we have agreed aims, and if the evidence considered is the same, and the ways of combining evidence are the same, then two or more people or groups should come to the same conclusions. If the conclusions are different, then the aims must be different, or the evidence considered must be different, or the ways of combining the evidence must be different. These differences should be discussed, debated and resolved.

In some areas, policy documents are subjected to the test of "soundness", where to be "sound" the strategy should be [4]

• justified i.e. "founded on a robust and credible evidence base" and "the most appropriate strategy when considered against reasonable alternatives"
  
• effective
  
• consistent with national policy
  

It is not clear to me why all policy documents are not subjected to this or a similar test of soundness.


In my opinion, those who care about decisions being made in the best possible way should always use the methods of science, should argue for their use, and should challenge any decision-making that is not based on evidence.

How do I justify this view on policy making?
I am not aware of scientific studies on policy making, and so I am only able to say that this seems to be the best answer to how to make policies.

I am putting forward a strategy for making policies and strategies, and so I should follow my own guidelines. The key thing is that the aims are (or should be) to give the public the best policies.

References

[1]	What works: evidence centres for social policy (2013) Cabinet Office, London https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/136227/What_Works_publication.pdf or from here
[2]	Making Evidence Useful (2013) Nesta http://www.nesta.org.uk/publications/assets/documents/making_evidence_useful
[3]	Consultation principles (2012) Cabinet Office, London https://www.gov.uk/government/publications/consultation-principles-guidance
[4]	The Planning Inspectorate (2009) Local Development Frameworks Examining Development Plan Documents: Soundness Guidance (2nd Edition) http://www.planningportal.gov.uk/uploads/pins/ldf_dpd_soundness_guide.pdf