The best method would probably be proportional odds regression using
polyr() in 'MASS'.
At least it's a starting point.
At 09:19 AM 6/22/2011, Matt Ellis \(Research\) wrote:
Hello,
I am struggling to figure out how to analyse a dataset I have inherited
(please note this was conducted some time ago, so the data is as it is,
and I know it isn't perfect!).
A brief description of the experiment follows:
Pots of grass were grown in 1l pots of standad potting medium for 1
month with a regular light and watering regime. At this point they were
randomly given 1l of one of 4 different pesticides at one of 4 different
concentrations (100%, 75%, 50% or 25% in water). There were 20 pots of
grass for each pesticide/concentration giving 320 pots. There were no
control (untreated) pots. The response was measured after 1 week and
recorded as either:
B1 - grass dead
B2 - grass affected but not dead
B3 - no visible effect
I could analyse this as lethal effect vs non-lethal effect (B1 vs B2+B3)
or some effect vs no effect (B1+B2 vs B3) binomial model, but I can't
see how to do it with three levels.
Any pointing in the right direction greatly appreciated!
Thanks
Matt
--------------------------------------------------------------------------
Disclaimer: This email and any files transmitted with it are
confidential and intended solely for the use of the individual or
entity to whom they are addressed. If you have received this email
in error please notify me at matt.el...@basc.org.uk then delete it.
BASC may monitor email traffic. By replying to this e-mail you
consent to BASC monitoring the content of any email you send or
receive from BASC. Any views expressed in this message are those of
the individual sender, except where the sender specifies with
authority, states them to be the views of the British Association
for Shooting and Conservation. BASC can confirm that this email
message and any attachments have been scanned for the presence of
computer viruses but recommends that you make your own virus checks.
Registered Industrial and Provident Society No.: 28488R. Registered
Office: Marford Mill, Rossett, Wrexham, LL12 0HL.
--------------------------------------------------------------------------
[[alternative HTML version deleted]]
______________________________________________
R-help@r-project.org 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.
================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: r...@lcfltd.com
Least Cost Formulations, Ltd. URL: http://lcfltd.com/
824 Timberlake Drive Tel: 757-467-0954
Virginia Beach, VA 23464-3239 Fax: 757-467-2947
"Vere scire est per causas scire"
______________________________________________
R-help@r-project.org 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.
