Conditioning on a Collider, Human Popsicle Edition

| Gabriel |

Robin Hanson mentions a poll of whether people would like to be cryogenically frozen and notes that the rate is higher for people outside the US, who he assumes are American expats and uses that as an argument about adventurous personality types. I’m skeptical that most of these people are American citizens as compared to foreigners who speak English, but let’s put that aside. The big problem is that this is a self-selected reader poll.

The short version of the problem is that reader polls are nearly worthless. The long version is that you’d expect to find a negative correlation between access to the poll and salience of its subject matter. Assume that there are two things driving participation in a reader poll:

1. Accessibility of the poll. In this case, the poll was hosted by ABC News, an American news organization that is presumably of greatest interest to people living in the US.
2. Salience of the poll’s subject matter. It’s pretty easy to imagine that cryonics fans may seek out material about cryonics. Some of them might have Google News alerts. Likewise it’s not exactly unheard of for fans of a band/politician/whatever to find out about a reader poll and direct other fans to it. Note that I’m assuming that for this issue salience is highly correlated with favorability.

If so, the magic of conditioning on a collider means that the subset of the population that responds to the reader poll will have an artifactual negative correlation between accessibility and salience. Anytime that censorship is related to the interaction of two variables then the observed data suffer artifactual results about the relationship between those two variables (and their close correlates).

That’s it. We’re done. No need to speculate about Indiana Jones and the Freezer Burn of Doom.

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Misc Links

| Gabriel |

• Useful detailed overview of Lion. The user interface stuff doesn’t interest me nearly as much as the tight integration of version control and “resume.” Also, worth checking if your apps are compatible. (Stata and Lyx are supposed to work fine. TextMate is supposed to run OK with some minor bugs. No word on R. Fink doesn’t work yet). It sounds good but I’m once again sitting it out for a few months until the compatibility bugs get worked out. Also, as with Snow Leopard many of the features won’t really do anything until developers implement them in their applications.
• I absolutely loved the NPR Planet Money story on the making of Rihanna’s “Man Down.” (Not so fond of the song itself, which reminds me of Bing Crosby and David Bowie singing “Little Drummer Boy” in matching cardigans). If you have any interest at all in production of culture read the blog post and listen to the long form podcast (the ATC version linked from the blog post is the short version).
• Good explanation of e, which comes up surprisingly often in sociology (logit regression, diffusion models, etc.). I like this a lot as in my own pedagogy I really try to emphasize the intuitive meaning of mathematical concepts rather than just the plug and chug formulae on the one hand or the proofs on the other.
• People are using “bimbots” to scrape Facebook. And to think that I have ethical misgivings about forging a user-agent string so wget looks like Firefox.