Publications by R on The broken bridge between biologists and statisticians
Fitting ‘complex’ mixed models with ‘nlme’: Example #2
A repeated split-plot experiment with heteroscedastic errors Let’s imagine a field experiment, where different genotypes of khorasan wheat are to be compared under different nitrogen (N) fertilisation systems. Genotypes require bigger plots, with respect to fertilisation treatments and, therefore, the most convenient choice would be to lay-out ...
9449 sym R (3516 sym/19 pcs)
Fitting ‘complex’ mixed models with ‘nlme’: Example #4
Testing for interactions in nonlinear regression Factorial experiments are very common in agriculture and they are usually laid down to test for the significance of interactions between experimental factors. For example, genotype assessments may be performed at two different nitrogen fertilisation levels (e.g. high and low) to understand whether...
10729 sym R (4868 sym/7 pcs) 8 img
Fitting ‘complex’ mixed models with ‘nlme’: Example #4
Testing for interactions in nonlinear regression Factorial experiments are very common in agriculture and they are usually laid down to test for the significance of interactions between experimental factors. For example, genotype assessments may be performed at two different nitrogen fertilisation levels (e.g. high and low) to understand whether...
10560 sym R (3862 sym/7 pcs) 8 img
Fitting ‘complex’ mixed models with ‘nlme’: Example #3
Accounting for the experimental design in regression analyses In this post, I am not going to talk about real complex models. However, I am going to talk about models that are often overlooked by agronomists and biologists, while they may be necessary in several circumstances, especially with field experiments. The point is that field experiments...
7638 sym R (8606 sym/11 pcs) 4 img
Fitting ‘complex’ mixed models with ‘nlme’: Example #2
A repeated split-plot experiment with heteroscedastic errors Let’s imagine a field experiment, where different genotypes of khorasan wheat are to be compared under different nitrogen (N) fertilisation systems. Genotypes require bigger plots, with respect to fertilisation treatments and, therefore, the most convenient choice would be to lay-out ...
9310 sym R (3516 sym/19 pcs)
Nonlinear combinations of model parameters in regression
Nonlinear regression plays an important role in my research and teaching activities. While I often use the ‘drm()’ function in the ‘drc’ package for my research work, I tend to prefer the ‘nls()’ function for teaching purposes, mainly because, in my opinion, the transition from linear models to nonlinear models is smoother, for beginn...
8875 sym R (5947 sym/8 pcs) 2 img
Nonlinear combinations of model parameters in regression
Nonlinear regression plays an important role in my research and teaching activities. While I often use the ‘drm()’ function in the ‘drc’ package for my research work, I tend to prefer the ‘nls()’ function for teaching purposes, mainly because, in my opinion, the transition from linear models to nonlinear models is smoother, for beginn...
8875 sym R (5997 sym/8 pcs) 2 img
Some everyday data tasks: a few hints with R (revisited)
One year ago, I published a post titled ‘Some everyday data tasks: a few hints with R’. In that post, I considered four data tasks, that we all need to accomplish daily, i.e. subsetting sorting casting melting In that post, I used the methods I was more familiar with. And, as a long-time R user, I have mainly incorporated in my workflow all...
7431 sym R (9546 sym/9 pcs)
Some everyday data tasks: a few hints with R (revisited)
One year ago, I published a post titled ‘Some everyday data tasks: a few hints with R’. In that post, I considered four data tasks, that we all need to accomplish daily, i.e. subsetting sorting casting melting In that post, I used the methods I was more familiar with. And, as a long-time R user, I have mainly incorporated in my workflow all...
7431 sym R (8027 sym/9 pcs)
Self-starting routines for nonlinear regression models
In R, the drc package represents one of the main solutions for nonlinear regression and dose-response analyses (Ritz et al., 2015). It comes with a lot of nonlinear models, which are useful to describe several biological processes, from plant growth to bioassays, from herbicide degradation to seed germination. These models are provided with self-...
6835 sym R (3482 sym/10 pcs) 4 img