[RsR] use of lmrob() on ecological time series

[Emily Klein]

Dear all,

I am using the lmrob() function from the robustbase package, and I have a
few questions. To keep the threads clear, I have a general inquiry here,
and will ask more specific Qs in a second thread. NB: I don't typically
update in the middle of a project, so am running on R version 3.4.1.

(1) I am curious the community's thoughts on our approach: We have several
hundred ecological time series and we're using robust linear models to
determine if the time series are increasing, decreasing, or not changing,
by looking at the modeled slope. This approach follows several others,
including Lotze et al. 2017 (doi: 10.1111/cobi.12957) and Magare et al.
2013 (doi:10.1371/journal.pone.0077908). I don't have much experience with
RLMs, so any thoughts on this approach would be very welcome.

More specifically, following the work noted above, we are running (with the
time series indexed with "DBx"):
lm_test<-lmrob(log(pop_status+1)~observation_year,DBx)

(2)  Previous use of RLMs to identify the direction of ecological time
series was asked in peer review to use "non-significant change" to
reference time series with a slope of zero within the 95% confidence
intervals. I can see excluding time series where there is no agreement on
the direction of slope, but I think that slope=0 is more "stable" or "no
change" and is not necessarily "non-significant". Any thoughts?

Thank you all very much for any feedback you may have. I will start a
second thread on a few warnings I am getting.

Emily

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Emily S. Klein, Senior Postdoctoral Associate (she / her / hers)
The Frederick S. Pardee Center for the Study of the Longer-Range Future |
Boston University
*Co-Chair*, ICES Working Group on the History of Fish & Fisheries (WGHIST)
esklein04 using gmail.com

http://www.bu.edu/pardee/
http://www.ices.dk/community/groups/Pages/WGHIST.aspx

	[[alternative HTML version deleted]]