Monthly Archives: March 2012

Real Academic Work?

James McGrath left this nasty comment on P.Z. Myers’ blog about Richard Carrier and his use of Bayes’ theorem:

PZ, I have to say that I am very disappointed to find someone who stands for mainstream science against its bogus pseudoscientific critics, cheering on someone who represents the equivalent in the domain of history.

I’ve tried to offer some explanations regarding why Carrier’s attempt to engage in denialism ought to be found no more persuasive than the similar attempts to sow doubt regarding evolution, climate change, or anything else about which the vast majority of experts agree.

Evolution? Bayes’ Theorem. Climate Change? Bayes’ Theorem. Historical Jesus studies? Oh… well… when you attempt to use Bayes Theorem in that domain, you are the equivalent of a bogus pseudoscientific critic.

So make no mistake! Real academic work is not about method. It’s about appeals to authority and consensus.


Posted by on March 30, 2012 in Bayes


Epiphenom: Religious Students Have Fewer Interracial Friends

From here:

What she found was that the most religious students (based on self-reported religiosity, their frequency of religious service attendance, and their religious observance) also had the fewest friends from other races.

What’s more, Protestant or Jewish (but not Muslim, Hindu or Buddhist) students also had the fewest mixed-race friendships. That’s probably because these are the two major religious groups.

These two effects were independent – so the most mono-cultural people were the most religious Protestants and Jews. This held even after controlling for a bunch of other factors, including the racial diversity of the college, the diversity of their previous school, and the race of the student.

And on top of all this, belonging to a religious club reduced the chances of inter-racial friendship still further! That wasn’t the case with other clubs (except explicitly ethnic clubs – and even here the effect was smaller than for religious clubs).

Now, the interesting thing about these three factors – religiosity, religious denomination, and membership of a religious club – isn’t that they weren’t highly correlated. That means that they seem to have independent, additive effects.

I guess this makes sense in a way. It’s been well known for decades that there is a strong correlation between racism and religion. That is, the more religious someone is, the more likely it is that they’re racist. This is counterintuitive if you only look at the dogmas of religion and their pretense to inclusion, but we all know how well intuition works.

Of course my own anecdotal experiences confirm that religious people are more racist than the non-religious; a mother of an ex gf of mine apparently disapproved of interracial relationships (which was ours, but she didn’t know about it) and was one of the reasons why she didn’t approve of Obama, who was running for president at the time. Other religious parents of friends of mine also didn’t approve of interracial relationships going so far as to disown children for marrying outside of their race.

This probably isn’t a knock on religion per se; it probably means that racism and religion both appeal to the same sort of brain module that separates us vs them. This is evidenced by the fact that there is also a relationship between religiosity and nationalism. So it could be that people become religious just because they are also the type of people who are predisposed to racism and nationalism.

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Posted by on March 29, 2012 in cognitive science


French commune home to 20,000 ‘doomsday cultists’ awaiting alien salvation

I mean…

An estimated 20,000 New Age believers who say the “upside down” mountain is home to aliens who will rescue them from an impending apocalypse have saturated a small French commune near the foot of the picturesque Pic de Bugarach.

What is this I don’t even

“The apocalypse we believe in is the end of a certain world and the beginning of another,” one of the New Age pilgrims going only by the name “Jean,” tells the paper. “A new spiritual world. The year 2012 is the end of a cycle of suffering. Bugarach is one of the major chakras of the earth, a place devoted to welcoming the energies of tomorrow.”

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Posted by on March 28, 2012 in This is madness


The Existence Of Jesus Is Just A Theory

This should be the most common response to Creationists who insist that the theory of evolution is “just a theory”. And that feeling of being taken aback when you say “well, Jesus is just a theory” is the same feeling that normal people get when Creationists say that “evolution is just a theory”.

Make no mistake. Jesus is a hypothetical construct posited to make sense of Christianity, much in the same way the theory of evolution is posited to make sense of biology. The evidence for evolution is much better than the evidence for the existence of Jesus. So if Creationists want to doubt the theory of evolution because it’s “just a theory”, then they should be even more doubtful of the existence of Jesus based on the same logic. This is based on the simple fact that the hard sciences have more evidence to work with than history.

On the flip side of that, if the existence of Jesus is beyond reasonable doubt for the Creationist, then how much more solid is the existence of evolution? They are really stuck between a rock and a hard place if they assert that one is open to questioning and the other one is beyond questioning. This statement should really expose the hypocrisy of their “it’s just a theory” statement.

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Posted by on March 27, 2012 in apologetics, creationism, jesus myth


The Lord Works In Mysterious Way

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Posted by on March 26, 2012 in Funny


The Problem With Ad Hoc Hypotheses (Bayes’ Theorem And Coin Flips)

This post was originally part of a longer post I’m writing which is a follow up to these two posts. But I thought it would be good to dedicate a single post to it because I think it’s an important concept.

For Bayes’ theorem, evidence can only support hypotheses. Hypotheses can be used to support other hypotheses, but unlike evidence, this usually brings down the probability. Right now I’m having a bit of a discussion on my Facebook with someone who believes in ghosts. He says he knows he’s been haunted and been in haunted houses, therefore there is more to life than this universe because there are
other planes of existence. My response was that I thought it was more likely that he was mistaken about his encounter with ghosts instead of the human mind being immortal and entire other planes of existence being true.

It’s hard to get people to understand why his reasoning is wrong. He is stacking multiple hypotheses to explain an event. I didn’t disagree that he experienced something, but his interpretation of that experience is what I was questioning. I kept my explanation simple since I didn’t need to posit any other hypothesis besides human fallibility, which we all know is a large number.

When you add hypotheses to explain some event, the probability of each of those hypotheses has to be multiplied together. When a hypothesis is no longer hypothetical, that is, when we have confirmation of it and it becomes unquestioning fact, *that* is when you can add it as evidence for some initial hypothesis. And that is when you use Bayes’.

For example, in order to flip a coin and get three flips of heads in a row, I would have to first flip two heads in a row. In order to flip two heads in a row I have to flip heads on the first flip. Three heads depends on two heads which depends on one heads. Since the probability of flipping heads once is .5, and each additional heads depends on the previous heads, they all multiply together: .5 * .5 * .5 = .125.

In this case, .125 is the prior probability of flipping three heads in a row. What then happens once I flip heads once? It becomes:

P(H) = prior probability of flipping three heads in a row, .125
P(E) = probability of flipping heads, .5
P(E | H) = probability of flipping heads given that I will flip three heads in a row, 1.00 (it is absolutely necessary to flip heads given that I will flip three heads in a row)
P(E | ~H) = probability of flipping heads given that I won’t flip three heads in a row, ??? (not really necessary since I already know P(E), though it can be figured out as I demonstrated in the other two posts).

What is the probability that I will flip three heads in a row given that I have flipped heads once?

P(Flipping Three Heads In A Row | Flipping Heads Once) = P(E | H) * P(H) / P(E)
= 1.00 * .125 / .5
= .125 / .5
= .25

Given that I have flipped heads once, my prior has moved from .125 to .25. Which is what we would expect, since all we are really doing is subtracting one of the .5 probabilities from the three coin flips .5 * .5 * .5 and end up with only two flips to go — .5 * .5 — which equals .25.

And of course, absence of evidence is evidence of absence; I posted the Bayes’ theorem formula for that adage:

P(H | ~E) = P(~E | H) * P(H) / P(~E)

P(~E | H) is the compliment to P(E | H), both have to equal 1.00. Since P(E | H) in this example is already 1.00, this leaves nothing left for P(~E | H). Now we go through the anti-Bayes’ for absence of evidence:

P(H | ~E) = P(~E | H) * P(H) / P(~E)
= 0 * .125 / .5
= 0 / .5
= 0

So upon flipping tails, or the absence of the evidence of flipping heads, my prior probability of flipping three heads in a row plummets to zero.

Back to the ghost hypothesis to explain whatever it was that my friend experienced, he is doing the equivalent of flipping heads three times in a row. I have only flipped heads once. Notice the chain of probability:

1. Experience I can’t explain
2. It must be ghosts
3. Other planes of existence

Only 1 is in evidence. 2 is the explanation for 1, and 3 is the explanation for 2. The experience happened, so that is in evidence. The existence of ghosts is a hypothetical used to explain the experience, and the other planes of existence is a hypothetical used to explain ghosts. Since those two hypotheses aren’t in evidence, their probability — whatever they are — gets multiplied together just like the coin flips. If each of them was 60% probable, his ghost hypothesis used to explain the event is only 36% probable.

On the other hand, my chain of reasoning went like this:

1. Experience he can’t explain
2. The ghost explanation is probably hyperactive agency detection

Again, only 1 is in evidence. 2 is just the alternative to his ghost explanation and is 1 – P(Ghosts). In the above I assumed 60%, so this would be 40%. Since my total hypothesis has a 40% chance of being true, and his total hypothesis has a 36% chance of being true, my explanation is more probable even though I favored his hypothesis much more than I should have (60% probability that ghosts exist? 60% probability of another plane of existence? Really?).

In discussions with people, it’s important to distinguish between evidence and hypotheses. Evidence is anything that is factual, and the hypothesis is whatever framework is used to explain those facts. Lots of people equivocate between the two. If someone keeps adding hypotheticals to explain some event, this will exponentially lower the probability of their initial hypothesis being true. That is the problem with ad hoc hypotheses, and why Occam’s Razor makes sense.

For example, in historical Jesus research, scholars apply criteriology to discover facts, but this is equivocating between fact and hypothesis. Criteriology can only determine hypotheticals; the probability that some saying or event actually happened. Anything discovered via criteriology is not firmly in the fact bin but in the hypothetical bin. People can disagree about the cogency of some hypothetical, but no one should disagree about certain facts (“people are entitled to their own opinions but not their own facts”).

Even though both facts and hypotheticals have a certain probability, their probabilities are not utilized in the same way as hopefully the coin flip analogy showed.


Posted by on March 24, 2012 in Bayes


The Possible Therefore Probable Fallacy

The possible therefore probable fallacy. This is something that I have often encountered so many times in religious debates that there is no way I could put a finger on when I first ran into it. Not only that, but it was hard to explain why it was fallacious before I started studying probability theory. And there was no official name for this fallacy.

But make no mistake. It’s a fallacy. If you study probability theory, you will learn that everything is possible. Everything. Even though everything is possible, not everything is probable. This is the heart of the matter; we should always go by whichever idea or explanation has the highest probability of being correct, since this will minimize the probability of us being incorrect. If we didn’t do that, then things like the Base Rate Fallacy wouldn’t be, well, a fallacy.

The way it goes, someone posits some hypothesis that has a high probability of being correct. The person on the losing side, not content with being on the low end of the probability stick, spouts out his sore-loser argument: “I have this alternative argument. Even if it’s less probable than your argument it’s still possible! Therefore it’s true/I’m justified in believing it/na-na-nah-boo-boo.” While not as obvious as that, this is the basic gist of the thread of conversation.

Since Richard Carrier has recently published his book Proving History (p 26 – 29), there is now an actual peer reviewed publication that addresses this fallacy. Which means it is now an “official” fallacy since he gave it a Latin name lol: Possibiliter ergo probabiliter.

This can be added to the list of fallacies that can be analyzed by Bayes’.

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Posted by on March 23, 2012 in Bayes

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