# Multiple Factor Explanations Should Not Appear One-Sided

In [Policy Debates Should Not Appear One-Sided](/lw/gz/policy_debates_should_not_appear_onesided/), Eliezer Yudkowsky argues that arguments on questions of fact should be one-sided, whereas arguments on policy questions should not:

> On questions of simple fact (for example, whether Earthly life arose by natural selection) there's a legitimate expectation that the argument should be a one-sided battle; the facts themselves are either one way or another, and the so-called "balance of evidence" should reflect this.  Indeed, under the Bayesian definition of evidence, "strong evidence" is just that sort of evidence which we only expect to find on one side of an argument.
> 
> But there is no reason for complex actions with many consequences to exhibit this onesidedness property.

The reason for this is primarily that natural selection has caused all sorts of observable phenomena. With a bit of ingenuity, we can infer that natural selection has caused them, and hence they become evidence for natural selection. The evidence for natural selection thus has a common cause, which means that we should expect the argument to be one-sided.

In contrast, even if a certain policy, say lower taxes, is the right one, the rightness of this policy does not cause its evidence (or the arguments for this policy, which is a more natural expression), the way natural selection causes its evidence. Hence there is no common cause of all of the valid arguments of relevance for the rightness of this policy, and hence no reason to expect that all of the valid arguments should support lower taxes. If someone nevertheless believes this, the best explanation of their belief is that they suffer from some cognitive bias such as the [affect heuristic](/lw/lg/the_affect_heuristic/).

(In passing, I might mention that I think that the fact that moral debates are not one-sided indicates that moral realism is false, since if moral realism were true, moral facts should provide us with one-sided evidence on moral questions, just like natural selection provides us with one-sided evidence on the question how Earthly life arose. This argument is similar to, but distinct from, [Mackie's argument from relativity](http://plato.stanford.edu/entries/moral-anti-realism/moral-error-theory.html).)

Now consider another kind of factual issues: multiple factor explanations. These are explanations which refer to a number of factors to explain a certain phenomenon. For instance, in his book _[Guns, Germs and Steel](http://en.wikipedia.org/wiki/Guns,_Germs,_and_Steel)_, Jared Diamond explains the fact that agriculture first arose in the [Fertile Crescent](http://en.wikipedia.org/wiki/Fertile_Crescent) by reference to no less than eight factors. I'll just list these factors briefly without going into the details of how they contributed to the rise of agriculture. The Fertile Crescent had, according to Diamond (ch. 8):

1.  big seeded plants, which were
2.  abundant and occurring in large stands whose value was obvious,
3.  and which were to a large degree hermaphroditic "selfers".
4.  It had a higher percentage of annual plants than other Mediterreanean climate zones
5.  It had higher diversity of species than other Mediterreanean climate zones.
6.  It has a higher range of elevations than other Mediterrenean climate zones
7.  It had a great number of domesticable big mammals.
8.  The hunter-gatherer life style was not that appealing in the Fertile Crescent

(Note that all of these factors have to do with geographical, botanical and zoological facts, rather than with facts about the humans themselves. Diamond's goal is to prove that agriculture arose in Eurasia due to geographical luck rather than because Eurasians are biologically superior to other humans.)

Diamond does not mention any mechanism that would make it less likely for agriculture to arise in the Fertile Crescent. Hence the score of pro-agriculture vs anti-agriculture factors in the Fertile Crescent is 8-0. Meanwhile no other area in the world has nearly as many advantages. Diamond does not provide us with a definite list of how other areas of the world fared but no non-Eurasian alternative seem to score better than about 5-3 (he is primarily interested in comparing Eurasia with other parts of the world).

Now suppose that we didn't know anything about the rise of agriculture, but that we knew that there were eight factors which could influence it. Since these factors would not be caused by the fact that agriculture first arose in the Fertile Crescent, the way the evidence for natural selection is caused by the natural selection, there would be no reason to believe that these factors were on average positively probabilistically dependent of each other. Under these conditions, one area having all the advantages and the next best lacking three of them is a highly surprising distribution of advantages. On the other hand, this is precisely the pattern that we would expect given the hypothesis that Diamond suffers from confirmation bias or another related bias. His theory is "too good to be true" and which lends support to the hypothesis that he is biased.

In this particular case, some of the factors Diamond lists presumably are positively dependent on each other. Now suppose that someone argues that all of the factors are in fact strongly positively dependent on each other, so that it is not very surprising that they all co-occur. This only pushes the problem back, however, because now we want an explanation of a) what the common cause of all of these dependencies is (it being very improbable that they all would correlate in the absence of such a common cause) and b) how it could be that this common cause increases the probability of the hypothesis via eight independent mechanisms, and doesn't decrease it via any mechanism. (This argument is complicated and I'd be happy on any input concerning it.)

Single-factor historical explanations are often criticized as being too "simplistic" whereas multiple factor explanations are standardly seen as more nuanced. Many such explanations are, however, one-sided in the way Diamond's explanation is, which indicates bias and dogmatism rather than nuance. (Another salient example I'm presently studying is taken from Steven Pinker's [_The Better Angels of Our Nature_](http://en.wikipedia.org/wiki/The_Better_Angels_of_Our_Nature). I can provide you with the details on demand.*) We should be much better at detecting this kind of bias, since it for the most part goes unnoticed at present.

Generally, the sort of "too good to be true"-arguments to infer bias discussed here are strongly under-utilized. As our knowledge of the systematic and [predictable](http://en.wikipedia.org/wiki/Predictably_Irrational) ways our thought goes wrong increase, it becomes easier to infer bias from the structure or pattern of people's arguments, statements and beliefs. What we need is to explicate clearly, preferably using probability theory or other formal methods, what factors are relevant for deciding whether some pattern of arguments, statements or beliefs most likely is the result of biased thought-processes. I'm presently doing research on this and would be happy to discuss these questions in detail, either publicly or via pm.

***Edit: Pinker's argument. **Pinker's goal is to explain why violence has declined throughout history. He lists the following five factors in the last chapter:

*   The Leviathan (the increasing influence of the government)
*   Gentle commerce (more trade leads to less violence)
*   Feminization
*   The expanding (moral) circle
*   The escalator of reason

He also lists some "important but inconsistent" factors:

*   Weaponry and disarmanent (he claims that there are no strong correlations between weapon developments and numbers of deaths)
*   Resource and power (he claims that there is little connection between resource distributions and wars)
*   Affluence (tight correlations between affluence and non-violence are hard to find)
*   (Fall of) religion (he claims that atheist countries and people aren't systematically less violen

This case is interestingly different from Diamond's. Firstly, it is not entirely clear to what extent these five mechanisms are actually different. It could be argued that "the escalator of reason" is a common cause of the other one's: that this causes us to have better self-control, which brings out the better angels of our nature, which essentially is feminization and the expanding circle, and which leads to better control over the social environment (the Leviathan) which in turn leads to more trade.

  

Secondly, the expression "inconsistent" suggests that the four latter factors are comprised by different sub-mechanisms that play in different directions. That is most clearly seen regarding weaponry and disarmament. Clearly, more efficient weapons leads to more deaths _when they are being used_. That is an important reason why World War II was so comparatively bloody. But it also leads to a lower chance _of the weapons actually being used_. The terrifying power of nuclear weapons is an important reason why they've only been used twice in wars. Hence we here have two different mechanisms playing in different directions.

  

I do think that "the escalator of reason" is a fundamental cause behind the other mechanisms. But it also presumably has some effects which increases the level of violence. For one thing, more rational people are more effective at what they do, which means they can kill more people if they want to. (It is just that normally, they don't want to do it as often as irrational people.) (We thus have the same structure that we had regarding weaponry.)

  

Also, in traditional societies, pro-social behaviour is often underwritten by mythologies which have no basis in fact. When these mythologies were dissolved by reason, many feared that chaous would ensue ("when God is dead, everything is permitted"). This did not happen. But it is hard to deny that such mythologies can lead to less violence, and that therefore their dissolution through reason can lead to more violence.

  

We shouldn't get too caught up in the details of this particular case, however. What is important is, again, that there is something suspicious with only listing mechanisms that play in the one direction. In this case, it is not even hard to find important mechanisms that play in the other direction. In my view, putting them in the other scale, as it were, leads to a better understanding of how the history of violence has unfolded. That said, I find DavidAgain's counterarguments below interesting.