[R] help with lmer,

[Douglas Bates]

On 4/11/07, Brendan Connors <bconnors at sfu.ca> wrote:
> Hi R-users:
>
> New to R and I am trying to run a GLM with random effects.
>
> I have 3 replicates ('Replicate) of counts of parasites ('nor.tot.lep')
> before and after an experiment ('In.Out'). When I run lmer I get the
> error messages (16 of each) below...
>
>  > lmer(nor.tot.lep ~ In.Out + (In.Out|Replicate),data=coho, family
> =tweedie(var.power = 1,
> + link.power = 1))
> Generalized linear mixed model fit using PQL
> Formula: nor.tot.lep ~ In.Out + (In.Out | Replicate)
> Data: coho
> Family: Tweedie(mu^1 link)
> AIC BIC logLik deviance
> 849.2 867.4 -419.6 839.2
> Random effects:
> Groups Name Variance Std.Dev. Corr
> Replicate (Intercept) 0.78861 0.88804
> In.Out 0.67232 0.81995 -1.000
> Residual 2.96308 1.72136
> number of obs: 279, groups: Replicate, 3

According to this summary you have 3 distinct replicates and you are
trying to use those three replicates to estimate 3 variance-covariance
parameters.  It won't work.  Notice that the estimated correlation is
-1.000.  Your estimated variance-covariance matrix is singular.

>
> Fixed effects:
> Estimate Std. Error t value
> (Intercept) -0.2431 0.6619 -0.3672
> In.Out 1.6004 0.5645 2.8349
>
> Correlation of Fixed Effects:
> (Intr)
> In.Out -0.975
> There were 30 warnings (use warnings() to see them)
>
>  > warnings()
> Warning messages:
> 1: Estimated variance-covariance for factor 'Replicate' is singular
> in: LMEopt(x = mer, value = cv)
> 2: nlminb returned message false convergence (8)
> in: LMEopt(x = mer, value = cv)
>
> I have made sure I have the latest lme4 version, any help would be much
> appreciated.
>
> Cheers,
>
> Brendan Connors
> Behavioural Ecology Research Group
>
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