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

[Robert Terwilliger]

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

Regards,

--
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/
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