You could analyze these data with a multinomial logit model, with an ordinal response. I don't have my copy handy, but I know that Agresti (Categorical Data Analysis, Wiley) covers these models.
Cheers David Cross d.cr...@tcu.edu www.davidcross.us On Jun 22, 2011, at 8:19 AM, 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. ______________________________________________ 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.
