lukeprog comments on Many Weak Arguments vs. One Relatively Strong Argument - Less Wrong

20 Post author: JonahSinick 04 June 2013 03:32AM

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Comment author: lukeprog 06 June 2013 12:10:20AM 18 points [-]

This is a messy subject, and one that's difficult write about, and I appreciate you tackling the topic. I think there are some important qualifications to make about this post, as others have noted. But I know that when writing about messy subjects, it's hard to avoid "death by a thousand qualifications." Lately, I've been trying to solve the problem by putting most qualifications in footnotes, e.g. here. You might want to try that, as it mitigates criticisms of the "but you didn't make qualifications X and Y!" form while still leaving the body text in a readable condition.

Below, I'll refer to MWA ("many weak arguments") and ORSA ("one relatively strong argument"), for convenience.

Here's my guess at what's going on:

  1. Probability theory doesn't "intrinsically favor" MWA over ORSA. Both have their uses, their limits, and their "gotchas" when applied to bounded rationality. If MWA is in some important sense "reliably better" than ORSA, I'd need stronger evidence/argument than is provided in this post. (That's not necessarily a criticism of the post; putting together strong evidence+argument about messy subjects is difficult and time-consuming.)
  2. For historical reasons, Less Wrong tended to attract people accustomed to ORSA thinking — which is common in e.g. mathematics and philosophy. Hence, LWers tend to make "too much reliance on ORSA"-type mistakes more often than they make the "too much reliance on MWA"-type mistakes.
  3. Givewell tends to emphasize the MWA approach, and has been remarkably successful at figuring out the parts of the world they're trying to understand. This impressed you, and helped you to realize that, like many mathematicians, you had been placing too much emphasis on ORSA thinking.
Comment author: JonahSinick 06 June 2013 02:02:21AM *  8 points [-]

Thanks for the feedback.

I think there are some important qualifications to make about this post, as others have noted.

My hunch is that most significant problem with the MWA approach is the assumption of (weak) independence, in the sense that in practice, when sophisticated use of MWA fails, it's usually because the weak lines of evidence are all being driven by the same selection effect. A hypothetical example that jumps to mind is:

A VC is evaluating a startup. He or she reasons

  1. The sector is growing
  2. My colleagues think that the sector is good to invest in
  3. On an object level, their plan looks good
  4. The people are impressive

and the situation is

Re: #1 — The reason that the sector is growing is because there's a bubble

Re: #2 — The reason that the VC's colleagues think that the sector is good to invest in is because, like the VC, they don't recognize that there's a bubble.

Re: #3 — The VC's views on the object level merit of the project are colored by the memes that have been spreading around that are causing the bubble

Re: #4 — The reason that impressive people are going into the sector is because there's a bubble, so everyone's going into the sector – the people's impressiveness isn't manifesting itself in their choosing a good focus.

I don't know whether this situation occurs in practice, but it seems very possible.

Givewell tends to emphasize the MWA approach, and has been remarkably successful at figuring out the parts of the world they're trying to understand.

GiveWell is an interesting case, insofar as it's done more ORSA work than I've seen in most contexts. The page on long lasting insecticide treated nets provides examples. Part of why I'm favoring MWA is because GiveWell has done both and of the two, leans toward MWA.

Comment author: RandomThinker 06 June 2013 04:48:51AM 4 points [-]

This is a great example. It's often very hard to tell whether MWA are independent or not. They could all derive from the same factors. Or they could all be made up by the same type of motivated reasoning.

I think that's the judgment of being a good "Fox" ala Tetlock's Hedgehog vs the Fox.

Comment author: Will_Sawin 13 June 2013 06:10:19AM 1 point [-]

Do you know ORSA that gets you out of this situation?

Comment author: JonahSinick 13 June 2013 06:22:30AM 0 points [-]

Which situation? The VC startup thing? The OSRA style is to scrutinize arguments carefully to see if they break down. If you can recognize that the arguments all break down in the same way, then you can conclude that the arguments are dependent and that even collectively, they don't constitute much evidence.

Comment author: Will_Sawin 13 June 2013 06:31:06AM 2 points [-]

But that still doesn't tell you whether to invest in the startup. If an ORSA-er is just paralyzed by indecision here and decides to leave VC and go into theoretical math or whatever, he or she is not really winning.

Unrelatedly, a fun example of MWA triumphing over ORSA could be geologists vs. physicists on the age of the Earth.

Comment author: JonahSinick 13 June 2013 03:56:52PM 0 points [-]

But that still doesn't tell you whether to invest in the startup. If an ORSA-er is just paralyzed by indecision here and decides to leave VC and go into theoretical math or whatever, he or she is not really winning.

I would guess that ORSA doesn't suffice to be a successful VC. The claim is that it could help, in conjunction with MWAs.

If you scrutinize the weak arguments and find that the break down in different ways, then that suggests that the arguments are independent, and that you should invest in the start-up. If you find that they break down in the same way, then that suggests that you shouldn't invest in the start-up.

Comment author: lukeprog 06 June 2013 02:14:48AM 1 point [-]

Part of why I'm favoring MWA is because GiveWell has done both and of the two, leans toward MWA.

I'd definitely be interested to learn (in more detail, with more examples) why this is. They may very well have good reasons for it.

Comment author: gothgirl420666 07 June 2013 10:23:49PM *  2 points [-]

For historical reasons, Less Wrong tended to attract people accustomed to ORSA thinking — which is common in e.g. mathematics and philosophy. Hence, LWers tend to make "too much reliance on ORSA"-type mistakes more often than they make the "too much reliance on MWA"-type mistakes.

Could you (or someone else) possibly give some examples of this? This seems like it's probably true but I'm having trouble thinking of concrete examples. I want to know the nature of the bias I should be compensating for.

Comment author: JonahSinick 06 June 2013 02:19:04AM *  1 point [-]

Probability theory doesn't "intrinsically favor" MWA over ORSA. Both have their uses, their limits, and their "gotchas" when applied to bounded rationality. If MWA is in some important sense "reliably better" than ORSA, I'd need stronger evidence/argument than is provided in this post.

  • It's true that both MWA and ORSA break down badly in certain, non overlapping, contexts.
  • I currently believe that MWA generally produces better predictive models about the human world than ORSA does. The context of the human world is a special one, and I would expect ORSA to systematically be better in some natural (not necessarily mathematical) contexts.
  • I believe that ORSA does outperform MWA in certain situations involving the human world (c.f. the remarks in my other comment about bubbles).
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