Hello R expert,

I have fish length and corresponding otolith size at six times for 30 fish. Firstly, I use a linear mixed effect model to correlate the fish length (L) with otolith size in dorsal radius (Dor). Since the residuals are domeshaped, I then tried to add a quadratic factor. However, as the summary shown below, the quadratic factor was missing in the analysis. WHY?

Thank you very much.

Lingbo


> back<-read.table("back.r", header=T)

> attach(back)

> names(back)

[1] "Fish"  "Treat" "Mark"  "L"     "Dor"   "Dis"   "Ven"   "Width"

> library(nlme)

> ldor.lme=lme(L~Dor, random=~1|Fish)

> ldor11.lme=lme(L~Dor+Dor^2, random=~1|Fish)

> summary(ldor11.lme)

Linear mixed-effects model fit by REML

 Data: NULL 

       AIC      BIC    logLik

  1539.336 1552.063 -765.6682

 

Random effects:

 Formula: ~1 | Fish

        (Intercept) Residual

StdDev:    31.90245 13.00981

 

Fixed effects: L ~ Dor + Dor^2 

                Value Std.Error  DF  t-value p-value

(Intercept) -30.74635  9.775326 149 -3.14530   0.002

Dor         157.14556  3.157083 149 49.77556   0.000

 Correlation: 

    (Intr)

Dor -0.797

 

Standardized Within-Group Residuals:

        Min          Q1         Med          Q3         Max 

-2.47279716 -0.59191227 -0.09822955  0.49939862  3.12757256 

 

Number of Observations: 180 

Number of Groups: 30 



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