I expect it would be hard to obtain good data about the actual results of implemented politics. (Not policies, which is a much more general term; just those policies adopted through a highly politicized process, like national laws or budget changes.)
This is for two reasons. First, major policy changes mostly happen when power changes hands, and a lot of changes happen together; their effects are hard to disentangle from one another.
Second, because most policies are attempts to influence human behavior. And people's reaction to political policies is itself politicized. People will react differently based on which party introduced a policy, or what other opinions it is publicly associated with.
This is just my prediction; I haven't checked it and I have no data to present in support.
So you're playing the credence game, and you’re getting a pretty good sense of which level of confidence to assign to your beliefs. Later, when you’re discussing politics, you wonder how you can calibrate your political beliefs as well (beliefs of the form "policy X will result in outcome Y"). Here there's no easy way to assess whether a belief is true or false, in contrast to the trivia questions in the credence game. Moreover, it’s very easy to become mindkilled by politics. What do you do?
In the credence game, you get direct feedback that allows you to learn about your internal proxies for credence, i.e., emotional and heuristic cues about how much to trust yourself. With political beliefs, however, there is no such feedback. One workaround would be to assign high confidence only to beliefs for which you have read n academic papers on the subject. For example, only assign 90% confidence if you've read ten academic papers.
To account for mindkilling, use a second criterion: assign high confidence only to beliefs for which you are ideologically Turing-capable (i.e., able to pass an ideological Turing test). As a proxy for an actual ideological Turing test, you should be able to accurately restate your opponent’s position, or be able to state the strongest counterargument to your position.
In sum, to calibrate your political beliefs, only assign high confidence to beliefs which satisfy extremely demanding epistemic standards.