I wonder to what extent politicians formulate policies based on models or make high level policies based on ideology or perceived voter preferences and then select the economic models to justify what they have already decided.

Edit: this isn't a comment about economics but how economics is used in a political context.

Of course they will have to take some decision even if they don't have a solid theory to back it up, but the problem today is that many governments try to make reality fit their idealized theories while it should be the other way around. I understand your point though, the lack of quantitative understanding of societal phenomena -on a national as well as international level- is a huge problem.