New feature coming to the game with the next update. The level of average minister effectiveness AND corruption both feed into the financial impact (cost/income) of policies and are now both shown at the bottom of the finance summary screens. Corruption costs!
Even better … this tooltip will now show you exactly how much the competence or otherwise of this minister is affecting this policies income or cost. Like a real-time incompetence-calculator for your cabinet! (also works for corruption)