Hi list members,

I am currently trying to run a series of linear mixed effects models using the lmer function in lme4, in order to compare models with fixed effects with null models. The models contain a series of nested and a crossed random effects in order to represent the structure of the hierarchic sampling campaign from which the data were collected. The code I'm using is:

mod1<-lmer(log10(MPP_TCB_mm3.l+0.1)~log10(TP)
 +(1|Country/WBID/StationID/SampleNumber)+(1|Analyst),REML=FALSE,data=phyto.data1)
null<-lmer(log10(MPP_TCB_mm3.l+0.1)~1
 +(1|Country/WBID/StationID/SampleNumber)+(1|Analyst),REML=FALSE,data=phyto.data1)
AIC(mod1,null)

However, when I run mod1 I get:
Warning message:
In mer_finalize(ans) : singular convergence (7)

I'm not familiar with this warning and so I am unsure of what to change to address the issue. Could anyone advise me on this? I could provide the data set if necessary.

All the best

Steve

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