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umxACEv - twin variance component

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a_researcher's picture
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Joined: 06/11/2021 - 12:53
umxACEv - twin variance component

Hi,

I was wondering if the umxACEv function allows the extension of the twin design to include the twin variance component, T? Thanks a lot!

tbates's picture
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Joined: 07/31/2009 - 14:25
umxACEv

Hi: Not sure I understand what you are asking: What is the "twin variance component" to which you refer?

a_researcher's picture
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Joined: 06/11/2021 - 12:53
ACET model

Hi, sorry for the lack of clarity--it would be T = environmental component specific to twins, which can be obtained also if siblings are included in the analysis (as an extended analysis): https://doi.org/10.1093/cercor/bhaa254.

a_researcher's picture
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Joined: 06/11/2021 - 12:53
Might there be any insight

Might there be any insight into this, or would it be more appropriate to use openmx directly specifically for this question?

AdminNeale's picture
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Joined: 03/01/2013 - 14:09
Beware of T

As a comment, note that variance that seems specific to twins because DZ twins correlate more than siblings could be due to age and cohort effects that decay the sibling correlation relative to the DZ twins. Even prenatally, maternal diet and stress likely differ more across pregnancies than it does across placentas in a twin pregnancy. That too could easily generate lower sib than DZ correlations. These processes seem inherently at least as likely as, e.g., people going "Ooooh they're twins, let's treat them really really similarly..." - this is especially difficult to do if you don't know a person is a twin :).