You're looking at Less Wrong's discussion board. This includes all posts, including those that haven't been promoted to the front page yet. For more information, see About Less Wrong.

Lumifer comments on Median utility rather than mean? - Less Wrong Discussion

6 Post author: Stuart_Armstrong 08 September 2015 04:35PM

You are viewing a comment permalink. View the original post to see all comments and the full post content.

Comments (86)

You are viewing a single comment's thread. Show more comments above.

Comment author: Houshalter 10 September 2015 12:08:00AM 0 points [-]

It can't be inconsistent within a world no matter how many decisions points there are. If we agree it's not inconsistent, then what are you arguing against?

I don't care about the VNM framework. As you said, it is designed to be optimal for decisions made in isolation. Because we don't need to make decisions in isolation, we don't need to be constrained by it.

Comment author: AlexMennen 10 September 2015 12:29:28AM 0 points [-]

If we agree it's not inconsistent...

No. Inconsistency between different possible worlds is still inconsistency.

Because we don't need to make decisions in isolation, we don't need to be constrained by it.

The difference doesn't matter that much in practice. If there are multiple decision points, you can combine them into one by selecting a policy, or by considering them sequentially and using your beliefs about what your choices will be in the future to compute the expected utilities of the possible decisions available to you now. The reason that the VNM framework was designed for one-shot decisions is that it makes things simpler without actually constraining what it can be applied to.

Comment author: Houshalter 11 September 2015 12:01:04AM 0 points [-]

No. Inconsistency between different possible worlds is still inconsistency.

It's perfectly consistent in the sense that it's not money pumpable, and always makes the same decisions given the same information. It will make different decisions in different situations, given different information. But that is not inconsistent by an reasonable definition of "inconsistent".

The difference doesn't matter that much in practice.

It makes a huge difference. If you want to get the best median future, then you can't make decisions in isolation. You need to consider every possible decision you will have to make, and their probability. And choose a decision policy that selects the best median outcome.

Comment author: AlexMennen 11 September 2015 01:05:02AM 0 points [-]

It's perfectly consistent in the sense that it's not money pumpable, and always makes the same decisions given the same information.

As in my previous example (sorry about it being difficult to follow, though I'm not sure yet what I could say to clarify things), it is inconsistent in the sense that it can lead you to pay for probability distributions over outcomes that you could have achieved for free.

You need to consider every possible decision you will have to make, and their probability.

Right. As I just said, "you can... consider them sequentially and use your beliefs about what your choices will be in the future to compute the expected utilities of the possible decisions available to you now." (edited to fix grammar). This reduces iterated decisions to isolated decisions: you have certain beliefs about what you'll do in the future, and now you just have to make a decision on the issue facing you now.