[R] gam function & time trend spline

[Roger Peng]

If you're looking only at winter days then you probably don't need to
remove seasonal trends, do you?

-roger

On 7/2/07, Kevin Sorensen <ksorensen84 at yahoo.com> wrote:
> I've been doing a simple time-series analysis looking
> at the relationship between daily pneumonia
> hospitalizations and daily temperature.  To mimic some
> of the literature, I've been including a time-trend to
> try to account for normal cyclical trends in
> hospitalization.  So I've been using a function that
> looks something like this:
>
> gam(pneucount ~ temp_f +
> s(day,bs="cr",k=(4*totalyears)+1),
>
> day being the enumerated day in the analysis (1-365
> for a 1 year analysis).
>
> This seems to work well enough.  What troubles me is
> when I think about doing an analysis focusing on
> winter days using more than one year of data.  If I
> just delete the summer days from the dataset, the time
> trend spline is trying to anneal counts from the end
> of one winter with the beginning of another, which
> doesn't seem right to me.
>
> What's the route to a statistically defensible result?
>  Is it as simple as using the subset option?  Or would
> I need to create indicator variables for each winter
> I'm interested and work in a by statement somehow
> (with an extra term for the levels of that indicator,
> I assume)?
>
> Thanks in advance for helping a Epi student who's
> being exposed to all this for the first time.
>
> Sincerely,
>
> Kevin Sorensen
>
>
>       ____________________________________________________________________________________
> Park yourself in front of a world of choices in alternative vehicles. Visit the Yahoo! Auto Green Center.
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Roger D. Peng  |  http://www.biostat.jhsph.edu/~rpeng/