[R-sig-ME] longitudinal analysis using lmer?

[Emmanuel Charpentier]

Le lundi 31 août 2009 à 12:53 -0400, Robert Terwilliger a écrit :
> Thanks everyone for all the advice.
> 
> One question I have (maybe there will be more...... :-P ):
> Should I exclude subjects that have only 1 or 2 data points?

The question you shuld try to answer is "*Why* do they have only 1 or 2
points ?".

HTH,

					Emmanuel Charpentier


> On Fri, Aug 28, 2009 at 7:07 PM, Ken Beath<ken-PJqznCQlsrTvnOemgxGiVw at public.gmane.org> wrote:
> > On 29/08/2009, at 6:07 AM, Robert Terwilliger wrote:
> >
> >> One more thing........
> >>
> >> What i sent was only a small sample of the data, just for the purpose
> >> of showing what kind of set we have.
> >>
> >> We have about 150 subjects, with starting ages between 8 and 21, with
> >> 3-5 data points (yearly visits) per subject.
> >>
> >
> > This will be fine, although it isn't as good as having a smaller number of
> > complete series. One point is that they don't look completely linear, so a
> > polynomial (maybe quadratic) or regression spline may be a better option.
> > Judging by the scatter the random effect variance will probably be close to
> > zero.
> >
> > Ken
> >
> >
> >
> >
> >> Thanks,
> >>
> >> --
> >> Robert Terwilliger
> >> Physicist
> >> Laboratory of Neurocognitive Development
> >> Western Psychiatric Institute and Clinic
> >> University of Pittsburgh Medical Center
> >> Loeffler Building
> >> 121 Meyran Avenue  #114
> >> Pittsburgh, PA 15213
> >> 412.383.8174  - Office
> >> 412.383.8179 - Fax
> >> em: raterwil at gmail.com
> >> http://www.wpic.pitt.edu/research/lncd/
> >>
> >> *******************************************************
> >> Dear R mixed effects gurus,
> >>
> >> I have the following data below. Attached is a png graphic
> >> representing the data.
> >>
> >> I would like to run the following analysis:
> >>
> >> signal ~ age | subject.
> >>
> >> For your information (not statically relevant), the "signal" variable
> >> is from a functional MRI experiment.
> >>
> >> At issue is whether this analysis is valid using "lme". From the graph
> >> (and the table below), one can see that there are five subjects.
> >> However, each subject begins at a different age. Subject 1 begins at 8
> >> and goes to 12, while subject 5 begins at 14. From my study of
> >> longitudinal analysis, usually each subject begins at the same
> >> starting point, while these data have subjects beginning at different
> >> starting points (different ages).
> >>
> >> Any insight is appreciated.
> >>
> >> subject age     signal
> >> 1       8       0.108
> >> 1       9       0.139
> >> 1      10    NA
> >> 1       11      0.151
> >> 1       12      0.148
> >> 2       10      0.127
> >> 2      11    NA
> >> 2       12      0.135
> >> 2       13      0.146
> >> 3       9       0.105
> >> 3       10      0.123
> >> 3       11      0.134
> >> 3       12      0.151
> >> 3       13      0.145
> >> 4       12      0.130
> >> 4       13      0.169
> >> 4       14      0.146
> >> 4       15      0.174
> >> 5       14      0.158
> >> 5       15      0.141
> >> 5       16      0.178
> >> 5      17    NA
> >> 5       18      0.172
> >>
> >> _______________________________________________
> >> R-sig-mixed-models at r-project.org mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-sig-mixed-models
> >>
> >
> >
> 
> 
>