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Error: In mer_finalize(ans) : false convergence (8)

ONKELINX, Thierry 
Sarah,

Always keep the mailing list in cc while replying.

After having a close look to you design I would suggest to go for one of the models below. If you are interested how the effect of TMT1 and TMT2 change in time go for Mod1. Go for Mod2 is you expect that their effect remains constant over time. Otherwise go for Mod3.

lmerdat$SpuplotID <- with(lmerdat, interaction(Block, TMT1, TMT2))
Mod1 <- lmer(log(Y) ~ TMT1 * TMT2 * Year + (1|Block/SubplotID), data = lmerdat, verbose = TRUE)
Mod2 <- lmer(log(Y) ~ TMT1 * TMT2 + (1|Block/SubplotID) + (1|Year), data = lmerdat, verbose = TRUE)
Mod3 <- lmer(log(Y) ~ TMT1 * TMT2 + (1|Block/SubplotID) + (0 + TMT1 :  TMT2|Year), data = lmerdat, verbose = TRUE)

Assuming Year is continuous Mod1 requires 10 parameters to be estimated. Your design yields 24 observations per year. Unless you have at least 4 years of data, the model is too complex for your data. You might want to look at the quote of Fisher in my signature...

Best regards,

ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest
team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
Kliniekstraat 25
1070 Anderlecht
Belgium
+ 32 2 525 02 51
+ 32 54 43 61 85
Thierry.Onkelinx at inbo.be
www.inbo.be

To call in the statistician after the experiment is done may be no more than asking him to perform a post-mortem examination: he may be able to say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can be extracted from a given body of data.
~ John Tukey


-----Oorspronkelijk bericht-----
Van: Sarah Dryhurst [mailto:s.dryhurst at gmail.com]
Verzonden: vrijdag 26 juli 2013 12:07
Aan: ONKELINX, Thierry
Onderwerp: Re: [R-sig-ME] Error: In mer_finalize(ans) : false convergence (8)

Dear Thierry,

Thanks so much for you reply,  Apologies - I should have explained the experiment better.  I have:

6 blocks
2 plots per block: one receiving one level of TMT1, one as a TMT1 control
2 subplots per plot: one receiving TMT2, one as TMT2 control.

The response is a measure of biomass (production) in each subplot I tried removing it as a fixed effect as you suggested, and the model does indeed converge.  However I'm interested in the effects of both
TMT1 and TMT2 and how they might interact, so I want to retain TMT1 as both a fixed effect and a random effect nested with block (due to the nature of the design)...  Perhaps I could remove year as a fixed effect?  Forgive me if I am making a silly mistake here: still learning this stuff!

Thanks again

Sarah
On Fri, Jul 26, 2013 at 9:16 AM, ONKELINX, Thierry <Thierry.ONKELINX at inbo.be> wrote:
--
NERC PhD Student
Community Ecology and Global Change
Department of Biology
Imperial College, London
email: sarah.dryhurst08 at imperial.ac.uk
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Thread (4 messages)

ONKELINX, Thierry Error: In mer_finalize(ans) : false convergence (8) Jul 26 Sarah Dryhurst Error: In mer_finalize(ans) : false convergence (8) Jul 26 ONKELINX, Thierry Error: In mer_finalize(ans) : false convergence (8) Jul 26 Sarah Dryhurst Error: In mer_finalize(ans) : false convergence (8) Jul 26