The Smoking Lesion: A problem for Evidential Decision Theory
This is part 3 of a sequence titled “Less Wrong and decision theory”
The previous post is “Newcomb’s Problem: A problem for Causal Decision Theories”
In the previous post, I discussed a flaw in Causal Decision Theory due to Newcomb’s Problem which started off a lot of discussion on whether it was rational to one or two box on Newcomb’s Problem. I believe that it is the majority view on Less Wrong that one boxing is the rational decision. I also believe it is the majority view elsewhere that two boxing is the rational decision.
As this is a post for Less Wrong, I will continue to act as if a decision is rational if it leads to the best possible outcome. If you disagree with this then you could think of this exploration of decision theory as an attempt to explore what decision theory should motivate an artificial intelligence – in this case it seems more clear that we would want the agent to make the decisions that will deliver the greatest benefit. This leads us in to an investigation of another decision scenario: The Smoking Lesion.
The Smoking Lesion
The Smoking Lesion Problem is as follows: In the world of the Smoking Lesion, smoking is correlated with cancer but does not cause cancer. Instead, there is a genetic lesion which, if present, increases a person’s chance of smoking and their chance of developing cancer. The Lesion is either already present or not present. You do not know if it is present in you. The question is this, if you like to smoke (but strongly dislike having cancer), should you smoke?
The desired answer in this situation seems to be that you should smoke – doing so does not increase your chances of developing cancer and it gives you pleasure. What do causal and evidential decision theories do here?
Remember what Evidential Decision Theory looks for – it asks whether a decision would act as evidence for a possible outcome. So smoking would be evidence that you were more likely to have the genetic lesion. Thus, evidential decision theory would advise that you don’t smoke. Causal Decision Theory, meanwhile, would say that smoking has no causal effect on cancer and so you should feel free to smoke.
The failure of traditional decision theory
So this is a situation where Evidential Decision Theory fails. The previous post noted that Causal Decision Theory fails to provide the correct answer in Newcomb’s Problem. So due to these decision problems, it seems that traditional approaches to decision theories are flawed. These problems, and others like them, are the reasons why people on Less Wrong have focused so much attention on trying to develop new decision theories. The next post will explore other scenarios that can test these new theories.
Appendix 1: Other resources
“The smoking lesion” – entry on the Less Wrong wiki
Timeless decision theory and metacircularity – A post by Eliezer that deals with the Smoking Lesion problem among other topics
The next post is “Decision theories and strange scenarios”