Hi,I have tumor growth curve data for a bunch of different mice in various
groups. I want to compare the growth curves of the different groups to see if
timing of drug delivery changed tumor growth.I am trying to run a mixed models
with repeated measures over time with each mouse as a random effect with linear
and quadratic terms for time.This took me a long time to figure out and I just
wanted to make sure I did it correctly and I am interpreting it correctly. This
is the code I ran
Rtumor<-lmer(volume~Group+Time+(1|Subject),
data=Rtumor)summary(Rtumor)Rtumor.null=lmer(volume~Time+(1|Subject),
data=Rtumor, REML=FALSE)Rtumor.full=lmer(volume~Group+Time+(1|Subject),
data=Rtumor, REML=FALSE)anova(Rtumor.null,Rtumor.full)
Here is my output Rtumor<-lmer(volume~Group+Time+(1|Subject), data=Rtumor)>
summary(Rtumor)Linear mixed model fit by REML ['lmerMod']Formula: volume ~
Group + Time + (1 | Subject) Data: Rtumor
REML criterion at convergence: 1541.2
Scaled residuals: Min 1Q Median 3Q Max -1.8006 -0.6348
-0.0658 0.3903 4.7551
Random effects: Groups Name Variance Std.Dev. Subject (Intercept)
3.197e-09 5.654e-05 Residual 3.348e+05 5.786e+02Number of obs: 101,
groups: Subject, 11
Fixed effects: Estimate Std. Error t value(Intercept) -495.520
303.619 -1.632Group 24.350 115.615 0.211Time 79.653
7.886 10.101
Correlation of Fixed Effects: (Intr) Group Group -0.933 Time -0.300
-0.007
> Rtumor.null=lmer(volume~Time+(1|Subject), data=Rtumor, REML=FALSE)>
> Rtumor.full=lmer(volume~Group+Time+(1|Subject), data=Rtumor, REML=FALSE)>
> anova(Rtumor.null,Rtumor.full)Data: RtumorModels:Rtumor.null: volume ~ Time +
> (1 | Subject)Rtumor.full: volume ~ Group + Time + (1 | Subject) Df
> AIC BIC logLik deviance Chisq Chi Df Pr(>Chisq)Rtumor.null 4 1576.5
> 1586.9 -784.24 1568.5 Rtumor.full 5 1578.4 1591.5
> -784.22 1568.4 0.0457 1 0.8307There were 50 or more warnings (use
> warnings() to see the first 50)
My questions are1) Did I do this correctly?2) Do I still need to run it again
with quadratic terms for time?, If so, how do I do this?3) If I am
understanding these results correctly, they say There is no difference between
these groups on volume growth curves
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