unreplicated repeated measures

Dear R users,

Sorry if this question is not applicable to this site. I am having problems
analysing unreplicated repeated measures. I calculated food web properties
for three treatments over time (10 months). It is unreplicated in that I
only have one observation per month per treatment. My problem is that I am
interested in how a food web property varies between Treatments and over
time.

Originally I had tried using lmer:
m4<-lmer(lncon~Treatment*month+(1|month),data=dataset)
but this provides the following error for which I have not found an
explanation to on the R site.
Error in mer_finalize(ans) : Calculated PWRSS for a LMM is negative

I suspect it is because I had treated month as a factor and consequently due
to the lack of replication and trying to interact these two categorical
variables it fails. I can overcome this problem by treating month as a
continuous variable from which I calculated confidence intervals using MCMC
method. However I am not sure how these are being calculated and if this is
accurate, given I have no mean per Treatment as such. Is it acceptable to
use month as a continuous variable?

Alternatively, I tried using repeated measures ANOVA, aov, to model the
data. I am cautious to use this method as it indicates significant
differences which are not apparent from the plotted raw data. Given that my
data lacks replication, I am wary of this method.

I have investigated time series analysis, but I am reluctant to venture down
this route.

Any reassurance or advice as to the best technique given my data would be
greatly appreciated.

Many thanks,
Christine


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Christine