[R-sig-ME] A question

[sheida sarafzade]

Hello
I'm MSc. student in biostatistics and working on mixed effect models
I’m trying to add fitted line to scatter plot (x,y)
Here “weight” is dependent variable and “month” is time variable.
The program is:
Lme1<-Lme(weight~month+(month^2),data=DataSetName,random=~month|id)

When I use the code below:
Lines(month[order(month)],fitted.lme(lme1,level=0)[order(month)])

It draws a smooth line but when I add a covariate (like birth weight)
to my model as below:

Lme2<-lme(weight~BirthWeight+month+(month^2),data=DataSetName,random=~month|id)

And then write the code below:
Lines(month[order(month)],fitted.lme(lme2,level=0)[order(month)])

It doesn’t draw smooth line. the line is not smooth.

How can I fix this problem?
What is the role of term “level” in this code? And what are it’s option?

for more information please see attachment
Thanks a lot
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