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Douglas_Knight comments on Open thread, Mar. 2 - Mar. 8, 2015 - Less Wrong Discussion

4 Post author: MrMind 02 March 2015 08:19AM

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Comment author: Houshalter 03 March 2015 11:49:42PM 1 point [-]

I think I've found the core of our disagreement. I want an algorithm that considers all possible paths through time. It decides on a set of actions, not just for the current time step, but for all possible future time steps. It chooses such that the final probability distribution of possible outcomes, at some point in the future, is optimal according to some metric. I originally thought of median, but it can work with any arbitrary metric.

This is a generalization of expected utility. The VNM axioms require an algorithm to make decisions independently and Just In Time. Whereas this method lets it consider all possible outcomes. It may be less elegant than EU, but I think it's closer to what humans actually want.

Anyway your example is wrong, even without predetermined actions. The algorithm would buy bet A, but then not buy bet B. This is because it doesn't consider bets in isolation like EU, but considers it's entire probability distribution of possible outcomes. Buying bet B would decrease it's expected median utility, so it wouldn't take it.

Comment author: Douglas_Knight 05 March 2015 06:53:12PM 2 points [-]

The VNM axioms require an algorithm to make decisions independently and Just In Time.

No, they don't.

Comment author: Houshalter 07 March 2015 10:03:43AM -1 points [-]

Assuming the bet has a fixed utility, then EU gives it a fixed estimate right away. Whereas my method considers it along with all other bets that it's made or expects to make, and it's estimate can change over time. I should have said that it's not independent or fixed, but that is what I meant.

Comment author: Kindly 07 March 2015 03:11:39PM 1 point [-]

In the VNM scheme where expected utility is derived at a consequence of the axioms, the way that a bet's utility changes over time is that its utility is not fixed. Nothing at all stops you from changing the utility you attach to a 50:50 gamble of getting a kitten versus $5 if your utility for a kitten (or for $5) changes: for example, if you get another kitten or win the lottery.

Generalizing to allow the value of the bet to change when the value of the options did not change seems strange to me.