Genetic correlations that doesn't make sense

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No user picture. noamm Joined: 10/10/2018
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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!

Replied on Mon, 05/25/2020 - 17:56
Picture of user. tbates Joined: 07/31/2009

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.

Replied on Tue, 05/26/2020 - 08:55
No user picture. noamm Joined: 10/10/2018

In reply to by tbates

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!

Replied on Tue, 05/26/2020 - 14:03
Picture of user. AdminRobK Joined: 01/24/2014

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.