The advanced answer to this is to create conditional prediction markets. For example: a market for whether or not the Bank of Japan implements a policy, a market for the future GDP or inflation rate of Japan (or whatever your preferred metric is), and a conditional market for (GDP given policy) and (GDP given no policy).
Then people can make conditional bets as desired, and you can report your track record, and so on. Without a prediction market you can’t, in general, solve the problem of “how good is this prediction track record really” except by looking at it in detail and making judgment calls.
The advanced answer to this is to create conditional prediction markets. For example: a market for whether or not the Bank of Japan implements a policy, a market for the future GDP or inflation rate of Japan (or whatever your preferred metric is), and a conditional market for (GDP given policy) and (GDP given no policy).
Then people can make conditional bets as desired, and you can report your track record, and so on. Without a prediction market you can’t, in general, solve the problem of “how good is this prediction track record really” except by looking at it in detail and making judgment calls.