[R] means comparison with seasonal time series?

Thomas W Blackwell tblackw at umich.edu
Fri Aug 22 21:47:52 CEST 2003

Douglas  -

Your question is a bit beyond the scope of this list.
It's really at a level appropriate for an advanced graduate
student who is already doing a thesis in the area of time
series data.  Best thing is to see whether you can find some
consulting help from a local statistics department.

-  tom blackwell  -  u michigan medical school  -  ann arbor  -

On Fri, 22 Aug 2003, Douglas G. Scofield wrote:

> Dear R list,
> I have a sequence of weekly observations of number of adults and larvae
> in various size classes from a butterfly population living in a
> subtropical area with pronounced wet and dry seasons.  Wet and dry
> seasons are each defined 26 weeks long with fixed start and end dates.
> The data span 103 weeks (two seasons each of wet and dry) with some
> missing weeks.  What I would like to do is compare means of each type of
> observation between wet and dry seasons ("Does the number of adults
> observed vary by season?").  Not surprisingly there is pronounced
> autocorrelation in the data, e.g.:
>    dwtest(lm(numadults ~ week))
> gives
>    DW = 0.2727, p-value = < 2.2e-16
> Note that the effects of this autocorrelation extend across wet-dry and
> dry-wet boundaries.
> What would be a way to ask my questions in R?  It seems like I'd use
> nlme and define a corStruct, but it's unclear to me how I'd do that.
> I'm still learning R (and  statistics) so detailed answers would be most
> appreciated.
> Sincerely,
> Douglas Scofield                 Department of Biology
> d.scofield at umiami.edu            University of Miami
> off: (305) 284-3778              P.O. Box 249118
> fax: (305) 284-3039              Coral Gables, FL  33124-0421
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