We all know this ideal is far from reality, but in Is Decision-Based Evidence Making Necessarily Bad?, Sloan Mgmt Review offers 3 levels to define the role of evidence: 

• to make a decision – when data really does lead to a decision
• to inform a decision – when other factors such as judgment and bargaining play a role too
• to support a decision – when data is looked for that confirms the decision, and crucially, when disconfirming evidence is avoided or rejected.

They ...