Bayesian Biostatistics 2015

By | February 1, 2015

Authors: Petr Keil, Jan Smyčka This post contains materials for Bayesian stats course (2-4 Feb 2015 at Faculty of Science, Charles University, Prague, Czech Republic). The complete materials and their source codes (Markdown and R) are on my GitHub repository. The lectures can also be accessed directly as follows: DAY 1 Introduction: Course contents, pros… Read More »

Bayesian PCA

By | January 5, 2015

Authors: Jan Smycka, Petr Keil This post introduces experimental R package bPCA which we developed with Jan Smycka, who actually came with the idea. We do not guarantee the very idea to be correct and there certainly are bugs – we invite anyone to show us wrong, or to contribute. Rationale of bPCA Here is… Read More »

The cathedral, the bazaar, and the SNAFU principle

By | November 21, 2014

I've recently been exploring foundational ideas of Free and Open-Source Software (FOSS) culture, and I've found them relevant not only for software development, but also for academia. Here is something that I picked up for inspiration: If you have no idea who Richard Stallman is, I recommend his TEDx talk on Free software, free society.… Read More »

On Theory in Ecology – Reading Marquet et al. (2014)

By | October 27, 2014

Marquet et al. have essay in Bioscience entitled “On theory in ecology”, with the main message being we need more good theory; I agree 100%. The paper also presents an overview of important ecological theories and some good points about why theory is important. Notable one: “Theory, etymologically, comes from the ancient Greek theoria, which… Read More »

The man in the academic arena

By | October 20, 2014

Lately I went through a couple of ordinary academic failures. I had one manuscript rejected in three statistical journals in a row. I had another one rejected in Science, PNAS and PLoS Biology in a prompt sequence. Interestingly, among all of the six submissions only Science actually sent it out for review (and then rejected).… Read More »

Center for Theoretical Study, Prague: more intense than ivy league

By | October 8, 2014

I have recently been lucky to relocate from Yale to Center for Theoretical Study in Prague, Czech Republic. The institute brings together philosophers, mathematicians, physicists, sociologists, economists, biologists and others; it is similar to Santa Fe Institute or Princeton Institute for Advanced Study, and its aim is to stimulate interdisciplinary approaches to science, encouraging new… Read More »

Species Distribution Models on the right track. Finally.

By | September 2, 2014

Species Distribution Models (SDM) a.k.a. Niche Models have always been a busy pile of confusion, ideology and misguided practices, with the real mess being the “presence only” SDMs. Interestingly, when you go to conservation or biogeography symposiums, you can hear the established SDM gurus starting their talks with: “During the last ten years SDMs have… Read More »

Tailoring univariate probability distributions

By | June 26, 2014

This post shows how to build a custom univariate distribution in R from scratch, so that you end up with the essential functions: a probability density function, cumulative distribution function, quantile function and random number generator. In the beginning all you need is an equation of the probability density function, from which everyting else can… Read More »

Would you save the young or the ancient species?

By | March 14, 2014

Yesterday I gave a seminar at John Harte's lab at UC Berkeley. It was a joy. There must be something in the lush Californian climate that makes people nice. During the discussion John Harte and Andy Rominger jointly pointed me to a problem: Imagine that you have two species. The first one is a young… Read More »

Do 'macrosystems ecologists' know about macroecology?

By | February 18, 2014

Paper by Levy et al. in Frontiers in Ecology and the Environment announces emergence of a new ecological discipline called macrosystems ecology (MSE). The authors define MSE like this: MSE studies explore how broad-scale variation in fine-scale characteristics – such as organismal behavior and fitness, nutrient transformations, and water-use efficiency – relate to broad-scale spatial… Read More »

Spatial autocorrelation of errors in JAGS

By | February 10, 2014

In the core of kriging, Generalized-Least Squares (GLS) and geostatistics lies the multivariate normal (MVN) distribution – a generalization of normal distribution to two or more dimensions, with the option of having non-independent variances (i.e. autocorrelation). In this post I will show: (i) how to use exponential decay and the multivariate normal distribution to simulate… Read More »

Bayesian Biostatistics 2014

By | February 2, 2014

This post contains materials for Bayesian stats course that I taught between 2-4 Feb 2014 at Faculty of Science, Charles University, Prague, Czech Republic. There were around 40 participants. The complete materials and their source codes (Markdown and R) are on a GitHub repository. The lectures can also be accessed directly as follows (I recommend… Read More »

Making high-resolution biodiversity maps from low-res maps

By | October 23, 2013

This post advertises our new Ecological Applications paper which is in press. Imagine that there would be a tool that could make hi-res images out of low-res ones, just like this: Such tool would be really useful for creating maps of things for which we only have a very crude (low-res or coarse-grain) spatial information,… Read More »

The joy and martyrdom of trying to be a Bayesian

By | August 30, 2013

Some of my fellow scientists have it easy. They use predefined methods like linear regression and ANOVA to test simple hypotheses; they live in the innocent world of bivariate plots and lm(). Sometimes they notice that the data have odd histograms and they use glm(). The more educated ones use generalized linear mixed effect models.… Read More »

The effect of ski-pistes on butterflies

By | July 19, 2013

I have a weak spot for butterflies, and I love skiing. Every time I go up a ski lift I wonder how such a major landscape modification (ski pistes or ski slopes) affects nature. I have always had the impression that clear-cutting long and wide strips in mountain forests is not necessarily a bad thing.… Read More »