# Genetic correlations that doesn't make sense

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Joined: 10/10/2018 - 17:20
Genetic correlations that doesn't make sense

Hi, I'm trying to estimate a multivariate ACE model. I started by checking a correlated factors solution (umxACEv), but there are some correlations that just can't be real (e.g., 2.02).

rA1 rA2 rA3 rA4 rC1 rC2 rC3 rC4 rE1 rE2 rE3 rE4
x 1.00 1.00
y -0.40 1 0.17 1
z 0.03 0.38 1 -0.03 -0.03 1
w 0.15 2.02 -0.21 1 0.06 -0.41 -0.07 1

Standardized variance-based models may yield negative variances...
Warning message:
In sqrt(I * C) : NaNs produced

So I checked what are the computed correlations in a cholesky model (umxACE), and there are different correlations, in this case they are all in bounds, but still a correlation of 0.98 between two completely different variables, that were measured in two different ages, seem to be really weird. Furthermore, there are a lot of estimates that are drastically different both in magnitude (C correlations) and in direction, between the two models.

rA1 rA2 rA3 rA4 rC1 rC2 rC3 rC4 rE1 rE2 rE3 rE4
x 1.00 1.00 1
y -0.39 1 -0.11 1 0.16 1
z -0.07 0.27 1 -0.97 -0.15 1 . -0.02 1
w -0.20 0.98 0.25 1 -1.00 0.17 0.95 1 0.08 -0.33 -0.14 1

I'd appreciate any thoughts of why such values can occur.

Thanks!

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Joined: 07/31/2009 - 14:25
can't tell without the data

please share the MZ and DZ correlation tables.

I'm guessing this is some kind of oddity from small-n data

umxSummarizeTwinData() will generate the needed tables to say more.

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Joined: 10/10/2018 - 17:20
This seems the case indeed

This is the correlation table from umxSummarizeTwinData().

Var Mean SD rMZ (324) rDZ (635)
x 0.01 0.62 0.67 (0.06) 0.34 (0.06)
y -0.02 0.59 0.4 (0.08) 0.25 (0.06)
z 3.02 0.71 0.7 (0.03) 0.32 (0.04)
w 11.48 8.30 0.36 (0.16) 0.23 (0.14)

However, w comes from a different wave than the x and y. So when checking the overlap for w and y for example (the most out of bound correlation), there are only 15-17 families overlapping in MZ twins, so I'm guessing this is the explanation for the out of bounds correlations..

Thanks!

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Joined: 01/24/2014 - 12:15
parameterization
Standardized variance-based models may yield negative variances...
Warning message:
In sqrt(I * C) : NaNs produced

Based on the above, my guess is that the out-of-bounds correlations are a result of the A, C, and E matrices not being positive-definite under the parameterization (direct-symmetric?) being used. Since those matrices are not proper covariance matrices, their standardized forms won't be proper correlation matrices. There was a recent thread about that specifically.