# Negative estimates (such as A) - what to do if this corresponds to lowest AIC

I was wondering what one should do if the estimates of the model have a negative component for the variances of a given component. I am familiar that in the direct variance approach paper it mentions there can be negative A estimates, and this can make biological sense. Similarly, at least for the ACE/ADE base model, there is a negative/positive parameter estimate relationship in which interpretability should win out (so whichever one is positive here, since the AIC will be the same in any case for ACE/ADE). However, if the A estimate is negative, or any of the submodels have a negative estimate, and this corresponds to the lowest AIC, is there a potential explanation to this, other than that the model is not well-suited (given the paper itself mentions there can be negative A estimates and biologically this may be feasible)?

I appreciate it!

## One thing you might want to

HTH!

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In reply to One thing you might want to by AdminNeale

## Model selection

ACE: A) 15.33 [12.11, 18.16] C) <0.001 [-9.87, 9.87] E) 16·89 [14.89, 19.21]

ADE: A) -7.56 [-17.65, 17.65] D) 14·07 [-18.62, 18.62] E) 16.27 [14.23, 18.77]

I then tested the significance of the paths by comparing the submodes to the according full model and neither A, nor D were significant in the ADE model, but A was significant in the ACE model. I assume, in this case I should select the ACE model over the ADE model (even if the AIC is higher) and report the AE sub-model?

Thank you in advance!

Leslie

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In reply to Model selection by LeslieHeld

## Estimate ACE variance component model instead?

One thing you might try is to fit a model where the variance components are not constrained to be positive. See Verhulst & Neale. Also, it is useful to note the MZ and DZ correlations. In the long run, I don't think the approach to examine constrained-positive estimates in ACE vs ADE models is very sound statistically. If you fit the can-go-negative model, you may find that you get a negative estimate of C, which would indicate that the balance of C and D (including dominance AxA and higher order epistatic interactions) was such that the non-additivity outweighs the common environmental effects.

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In reply to Estimate ACE variance component model instead? by AdminNeale

## ACE and ADE have same -2lnL

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