Policy-based evidence making

Evidence-based policy making is a theoretical construct whereby political policy is based on sound scientific evidence. This doesn't happen a whole lot.

Policy-based evidence making, by contrast, happens all the time. Politicians have an idea, realise there is no scientific support for it, so set out to produce some.

Methods
The most common form of policy-based evidence making is opinion polls, which of course will always yield the result the pollsters are paid to deliver thanks to the miracle of push polling. Other forms of evidence generation exist too, including special committees set up to assess evidence and packed with the "right" people. Both of these practices have been repeatedly parodied in political shows like Yes, Minister and The Thick of It - and people have gone on record saying that both these shows are astoundingly accurate.

Working from a conclusion to provide only supporting evidence contradicts most interpretations of the scientific method but that doesn't bother the usual suspects: politicians and woo-merchants.

A shift to evidence-based policy?
The term "policy based evidence making" was referred to in a report of the House of Commons Select Committee on Science and Technology into Scientific Advice, Risk and Evidence Based Policy Making issued in October 2006. The committee stated:

[Ministers] should certainly not seek selectively to pick pieces of evidence which support an already agreed policy, or even commission research in order to produce a justification for policy: so-called "policy-based evidence making" (see paragraphs 95–6). Where there is an absence of evidence, or even when the Government is knowingly contradicting the evidence&mdash;maybe for very good reason&mdash;this should be openly acknowledged.

The UK government followed this advice pretty closely when, in 2009, they dismissed Prof. David Nutt from his advisory position on drugs for using objective, evidence-based standards to measure harm. Notably this led to him stating publicly that horse riding was more dangerous than ecstasy use (1 serious incident per 350 exposures, vs 1 serious incident per 10,000 exposures). Around the same time, the government also heeded advice to use evidence-based policy by reclassifying cannabis as a more dangerous drug than the evidence said it was.

Seriously, evidence-based policy just doesn't happen.

Quality polemics

 * "On the return of policy based evidence making," by the Adam Smith Institute.