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February 8th, 2008


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12:24 pm - An anthropologist's thoughts on bad science
This is what bad science look like. We have a study where genetics is supposedly more than twice as important than environment in determining obesity. I have no idea if this is true or not, and I have no more idea than I did before after looking at the study that supposedly proves this. The study uses 5,000 pairs of identical twins, and the article doesn't say so, I'm guessing they compared them to either non-identical twins or simply other siblings. The problem is that in most of the West, identical twins are subject to expectations about them being identical, and so there are significant behavioral similarities that are solely due to social expectations that non-twins do not face.

I've generally only seen two types of studies involving identical twins:

1) Studies, like this one, where the twins were raised together, and not only have the same environment, but also faced cultural expectations to be the same.

2) Studies where they were raised apart and did not know of one another. First off, this is vanishingly rare, and so most studies of this sort quite literally involve the same 2 dozen pairs of separated identical twins (thus resulting in a microscopic sample size). In addition, the only way to find twins where were raised separately is once they have found out about one another, so they have had months (or in most cases years) to spend time together and to work on developing habits in common, because identical twins are culturally expected to be identical.

The degree to which biologists and medical researchers discount culture is both impressive and deeply foolish.

(13 comments | Leave a comment)

Comments:


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From:hasufin
Date:February 8th, 2008 08:46 pm (UTC)
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I'm hesitant to call it bad science. The problem is that so very little methodology information is being reported. I have no way to evaluate the science, because I'm not being given any - just worthless factoids.
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From:heron61
Date:February 8th, 2008 08:55 pm (UTC)
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I've read enough similar studies in greater detail to be quite certain about the mistakes they are making. In similar studies the idea that comparing differences between identical twins and differences between twins and other siblings (or simply between other siblings) is a way to get at the differences between genetics and environment is fairly ubiquitous. If the researchers find fewer differences between twins than between other siblings, the assumption is that the lack of difference is due to genetic. I'd be literally shocked if this one was any different.
[User Picture]
From:hasufin
Date:February 8th, 2008 08:58 pm (UTC)
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That may well be - I'll admit that whenever I see the word "twin" in relation to a scientific study, I pretty much ignore the rest of it. It's just that this article doesn't actually given enough information to evaluate the scientific validity of the study. Which is it's own special flavor of sad, really.
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From:blue_estro
Date:February 8th, 2008 09:32 pm (UTC)
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See, we need to clone babies and separate them at birth. As we don't yet have the cultural expectation/conditioning that clones should behave the same way, when they find each other after the study it won't ruin their usefulness in future studies. :} Also, it would make for high viewership reality tv.

Silliness aside: To some extent all scientific survey based studies have to drop some potentially relevant information, as nothing is truly a closed system, but I agree that hard science tends to ignore sociology in general.

I am not sure that, outside of my unlikely cloning suggestion, that this study can be done with a high level of accuracy. It will always have some aspect of "bad science".
[User Picture]
From:rjgrady
Date:February 9th, 2008 03:58 am (UTC)
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I have seen some well controlled studies. They are fiendishly hard to do, and there is still that lingering doubt at the end. Like, there are some schizophrenia studies out there, but of course since you are looking at identical twins raised separarely from birth, you have to wonder about an interaction between adoption and vulnerability to schizophrenia. That is of course aside from non-chromosomal factors such as diet, mother's immune response, environmental exposure to subtances, systematic differences in the methodology of adoption agencies, etc.
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From:kitten_goddess
Date:February 8th, 2008 08:55 pm (UTC)
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I have not read the link. However, I think the study is a positive thing socially, because that means that people will stop seeing fat as evil or a sign of weak character. If people are willing to believe that something is genetic (whether or not it is), this means generally that whatever the "something" is, the people who have that trait will no longer be branded as sinners.

[User Picture]
From:tlttlotd
Date:February 9th, 2008 01:09 am (UTC)
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Remember that cross-disciplinary perspectives are strongly frowned upon.
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From:heron61
Date:February 9th, 2008 01:38 am (UTC)
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Heh, tell me about it... I was regarded as a very odd anthropology graduate student for wishing to also take sociology courses, and ultimately the difference between those two fields is whether you are studying inhabitants for the developed or developing world.
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From:aekiy
Date:February 9th, 2008 05:55 am (UTC)
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Interesting.. I'm constantly thinking about what I would want in a degree, and was recently considering a dual major in sociology and cultural anthropology. (My original idea was archeology.)

As for the twins thing.. I read recently that the first major study which most people cite about how similar twins are even when separated (took place in the '70s, I believe) was completely falsified. I would not be at all surprised to find that much of the studies since then have been biased by that paper and the lack of knowledge or understanding that it was a hack job by someone who just wanted a name.
From:nancylebov
Date:February 9th, 2008 01:38 am (UTC)
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And even twins who were raised apart had the same or nearly the same pre-natal environment, so some similarities between twins might not be genetic.
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From:athenian_abroad
Date:February 9th, 2008 04:45 am (UTC)
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From the paper (full text):
The present study had limitations. The twin method makes several assumptions, such as that monozygotic and dizygotic twins have similar environments. These assumptions have been discussed in detail elsewhere (25, 35, 36) To the extent that the environments (uterine or familial) of monozygotic twin pairs are more similar than those of dizygotic pairs, heritability estimates from twin studies will be inflated. However, existing evidence suggests that this effect is likely to be small and that it would not materially change the conclusion that phenotypic variation in adiposity is significantly determined by heritable genetic differences between persons.

[User Picture]
From:heron61
Date:February 9th, 2008 05:58 am (UTC)
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Thank you. It's now clear that they did simply decide to ignore culture, under the all too standard assumption that effects that might invalidate their experimental design. must naturally all be small enough to be ignored. Sigh...
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From:xuenay
Date:February 9th, 2008 12:29 pm (UTC)
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I also like the way that the news article proudly reports "weight is 77 percent attributable to genes"! Uhh, no. They found that weight is 77 percent heritable, under certain conditions in the UK. Heritability is always specific to a certain environment and subjects being studied - if everybody in the sample happens to be from a good environment, the majority of the variance must by definition come from the genes, and vice versa. You can't simply take a single study that reports a certain figure for heritability in one sample group and say that the heritability is the same everywhere. Just... no.

Argh, bad science reporting.

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