search for: allometr

Hello all, I'm fitting an allometric equation that looks like a really clean fit in the log-log space, but when I back transform the fit of the curve appears to need an adjustment - the fitted curve appears to predict values a good deal higher than those from the data. I included a bias correction per Newman, M. (1993). Regression...

Dear R helpers, For an allometric analysis (allometric equation y = a*x^b) I would like to apply a non-linear regression instead of using log-log transformations of the measured parameters x and y and a Model II linear regression. Since both of the variables x and y are random, I would like to apply a Model II non-linear anal...

Dear list members, I would like to know the difference in outputs and calculation processes between residuals.glm(object, type="response") and residuals.lm(object). For above-ground biomass estimation of trees, I estimated parameters of an allometric equation (ln y = b0 + b1*ln x) using glm as follows: fm <- glm(Ws~log(Wb), family=quasi(link="log", variance="mu")), where Ws and Wb are vectors containing the data of stem dry weight and branch dry weight(untransformed data, unit: kg), respectively. Here, I assumed tha...

Dear all, I've been reading for many days trying to predict with lmer but I haven't managed to do it. I've fitted an allometric model for trees where I have included climatic variables and diameter in the fixed part and in the random part I've included the experimental sites where trees are and also their provenance region. The model is like this : f431<-lmer(log(H05)~log(DN05)*(PwS+ PoS+ PpS+ TpS)+PoP:log(DN05)+P...

...tionship varies among sites, among families, and with tree size. These variance-partitioning desires push the analysis toward a mixed model framework. However, I am not interested in predicting twig density from trunk density, nor vice-versa. Rather, I'm interested in the slope of their allometric relationship. This makes a Major Axis fit highly desirable. However, slope.com() in the smatr package accepts only one grouping variable at a time (and no continuous covariates). Therefore, I've decided to fit the twig-trunk relationship with line.cis() and extract the residuals for...

Hello folks, I'm seeking opinions about the validity of the following use of the nls function... A colleague and myself are working with tree allometric data consisting of measurements of individual trees in semi-arid Australian woodland species. We need to make predictions of trunk diameter (DBH: diameter at breast height) given tree height and vice versa. I _think_ this falls into the category of model II regression in that both variables are m...

...error when I try to do pairwise comparisons between groups. Thank you, Ioulia -------- On Fri, May 11, 2012 at 2:09 AM, Ioulia Bespalova <bespa20i at mtholyoke.edu> wrote: > Hi there, > > I've been using the SMATR package to do standardized major axis (SMA) > regression on allometric data, and I've been able to to pairwise > comparisons of slope & elevation between multiple study sites. > > Now I'm trying to do the same thing using major axis (MA) regression, > but I'm getting errors (SMATR should be able to do MA as well as SMA > regression for...

Sorry, for disturbing the list again. > Also I got one suggestion of using ORDPACK at http://www.netlib.org/. It's ODRPACK at http://www.netlib.org/, not ORDPACK. Best, -- Etsushi Kato ekato at ees.hokudai.ac.jp -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send

Hi there, I've been using the SMATR package to do standardized major axis (SMA) regression on allometric data, and I've been able to to pairwise comparisons of slope & elevation between multiple study sites. Now I'm trying to do the same thing using major axis (MA) regression, but I'm getting errors (SMATR should be able to do MA as well as SMA regression for everything, right?) I&...