[R-sig-ME] Estimation of variance components in random- and mixed-effects models

[Thierry Onkelinx]

Another issue is that you have too few levels to fit "cohort" as a random
effect. I wrote a blogpost on this a few years ago:
https://www.muscardinus.be/2018/09/number-random-effect-levels/

Best regards,

ir. Thierry Onkelinx
Statisticus / Statistician

Vlaamse Overheid / Government of Flanders
INSTITUUT VOOR NATUUR- EN BOSONDERZOEK / RESEARCH INSTITUTE FOR NATURE AND
FOREST
Team Biometrie & Kwaliteitszorg / Team Biometrics & Quality Assurance
thierry.onkelinx using inbo.be
Havenlaan 88 bus 73, 1000 Brussel
www.inbo.be

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Op ma 28 jun. 2021 om 16:31 schreef Ben Bolker <bbolker using gmail.com>:

>    Are you using lme4? (I'm 99% sure you are, but it's good to be
> explicit.)
>
>    Are all of your fixed predictors numeric (rather than
> factor/categorical) ?
>
>    Note that a convergence warning is a *warning*, not an error: have
> you checked the troubleshooting steps in ?lme4::convergence (in
> particular, scaling and centering your predictor variables might help ...)
>
>    cheers
>     Ben Bolker
>
>
> On 6/28/21 10:17 AM, Amy Huang wrote:
> > Dear all,
> >
> > I am examining maternal effects, and my data have three hierarchy levels:
> > clutches of the same female, females, and cohorts. My explanatory
> variables
> > are at the female level (female length, age) and at the cohort level
> > (temperature).
> >
> > I would like to estimate the variance components of each hierarchy level
> > (i.e. relative amount of variance at each level) and then to find out
> which
> > factors (female length, age, temperature) explain most of the variance.
> For
> > these, I have two models:
> >      offspring trait ~ 1 + (1 | cohort/female/clutch)
> >      offspring trait ~ temperature + female length + age + (1 |
> > cohort/female/clutch)
> >
> > The major problem is that I only have 3 cohorts (and so 3 temperatures).
> >  From the first model I am able to get the information, but from the
> second
> > one there is an error message: "Model failed to converge with 1 negative
> > eigenvalue: -2.0e+01". The error pops up probably because I have both
> > temperature (fixed) and cohort (random) included. Is my approach correct?
> > And is there a way to fix this error?
> >
> > Thank you so much for your time.
> >
> > Best regards,
> > Amy Huang
> >
> >       [[alternative HTML version deleted]]
> >
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> >
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