Michael - Since your email says that the data are "the abundance of organism A", I am moved to ask whether the abundances are integer counts, sometimes zero, and whether the "samples" are perhaps dips of a net, or the contents of a filter after pumping a certain amount of water through it, or something akin to 'quadrats' in forest sampling.
If the abundances are integer counts, then it would be natural to analyze the data with a log-linear model using R's glm() rather than with anova. Snedecor and Cochran is an excellent book, but for this purpose Venables and Ripley's MASS (Modern Applied Statistics with S and S-plus) might be better. - tom blackwell - u michigan medical school - ann arbor - On Thu, 4 Mar 2004, Michael Rennie wrote: > Hi, all > > I have a rather un-ideal dataset that I am trying to work with, and would > appreciate any advice you have on the matter. > > I have 4 years worth of data taken at 3 depth-zones from which samples have > been taken at random. I am looking at the abundance of organism A between depth > zones and across years, and am interested in the possible interaction of > organism A distributions shifting between depth zones over time. Unfortunately, > the sample sizes (n) differ between depth zones, as follows: > > Year > 1 2 3 4 > Depth Zone 1 15 15 15 15 > 2 10 10 10 10 > 3 5 5 5 5 > > As such, I have a 2-way anova with unequal but proportional subclass numbers. > Sokal and Rolf (3rd Ed., 1995) have a nifty method of working out sums of > squares in this type of scenario (page 357, 358, box 11.6). However, they > don't tell you how to calculate the probabilities, but refer the reader on to > Snedecor and Cochran (1967), which I am on my way to consult shortly. > > I'm curious as to whether there is a more straightforward method of coding this > into R, rather than having to more or less customize my own statistical test. > I found some discussions in the archives revolving around type III sums of > squares from 2001, but the lack of consensus around the discussion did little > to assure me that I should try this approach. > > Anyone with advice, code or suggestions, I'd love to hear any of it. > > Cheers, > > Mike > -- > Michael Rennie > Ph.D. Candidate > University of Toronto at Mississauga > 3359 Mississauga Rd. N. > Mississauga ON L5L 1C6 > Ph: 905-828-5452 Fax: 905-828-3792 > ______________________________________________ > [EMAIL PROTECTED] mailing list > https://www.stat.math.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html > ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
