Hi.  I was wondering if anyone might have some suggestions about how I can
overcome a problem of   "iteration limit reached without convergence" when
fitting a mixed effects model.

 

In this study:

Outcome is a measure of heart action

Age is continuous (in weeks)

Gender is Male or Female (0 or 1)

Genotype is Wild type or knockout (0 or 1)

Animal is the Animal ID as a factor

Gender.Age is Gender*Age

Genotype.Age is Genotype*Age

Gender.Genotype.Age is Gender*Genotype*Age

 

If I have the intercept (but not the slope) as a random effect the fit
converges OK

fit1 <- lme(Outcome~Age + Gender + Genotype  + Gender.Age + Genotype.Age +
Gender.Genotype.Age,

                  random=~1|Animal, data=VC)

 

 

If I have the slope (but not the intercept) as a random factor it converges
OK

fit2 <- lme(LVDD~Age + Gender + Genotype + Gender.Age + Genotype.Age
+Gender.Genotype.Age,

                  random=~Age-1|Animal, data=VC)

 

 

If I have both slope and intercept as random factors it won't converge

fit3 <- lme(LVDD~Age + Gender + Genotype + Gender.Age + Genotype.Age +
Gender.Genotype.Age,

                  random=~ Age|Animal, data=VC)

Gives error:

Error in lme.formula(LVDD ~ Age + Gender + Genotype + Gender.Age +
Genotype.Age +  : 

      iteration limit reached without convergence (9)

 

 

 

If I try to increase the number of iterations (even to 1000) by increasing
maxIter it still doesn't converge

 

fit <- lme(LVDD~Age + Gender + Genotype + Gender.Age + Genotype.Age +
Gender.Genotype.Age,

+                   random=~ Age|Animal, data=VC, control=list(maxIter=1000,
msMaxIter=1000, niterEM=1000))

 

NB.  I changed maxIter  value in isolation as well as together with two
other controls with "iter" in their name (as shown above) just to be sure (
as I don't understand how the actual iterative  fitting of the model works
mathematically)  



 

I was wondering if anyone knew if there was anything else in the control
values I should try changing.   

Below are the defaults..

lmeControl

function (maxIter = 50, msMaxIter = 50, tolerance = 1e-06, niterEM = 25, 

    msTol = 1e-07, msScale = lmeScale, msVerbose = FALSE, returnObject =
FALSE, 

   gradHess = TRUE, apVar = TRUE, .relStep = (.Machine$double.eps)^(1/3), 

   minAbsParApVar = 0.05, nlmStepMax = 100, optimMethod = "BFGS", 

    natural = TRUE)

 

I was reading on the R listserve that lmer from the lme4 package may be
preferable to lme (for convergence problems) but lmer seems to need you to
put in starting values and I'm not sure how to go about chosing them.  I was
wondering if anyone had experience with lmer that might help me with this?

 

Thanks again for any advice you can provide.

 

Regards

Marg

 

 

Dr Margaret Gardiner-Garden

Garvan Institute of Medical Research

384 Victoria Street

Darlinghurst Sydney

NSW 2010 Australia

 

Phone: 61 2 9295 8348

Fax: 61 2 9295 8321

 

 


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