Archive for dynamical system

un des aspects surprenants des analyses et des commentaires sur l’épidémie de Covid-19 est l’absence de la statistique

Posted in Statistics, University life with tags , , , , , , , on May 6, 2020 by xi'an

From one French demographer (INED) in Le Monde [my translation], with a clustering of French departments into three classes [the figures on the above map are the lags after the first death in Haut-Rhin]:

One of the surprising aspects of the analyses and commentaries on the Covid-19 epidemic is the absence of statistics. Every evening, however, we are bombarded with figures, and many sites, from Public Health France (SpF) to Johns-Hopkins University (Maryland), abound in data.

But a number carries a meaning only in reference to other figures. This is where the real statistics start. However, apart from comparing the number of contagions and deaths by country and date, little has been learned from the data, which could provide useful information on the nature and progression of the epidemic (…)

We can see that the diversity of close contacts is one of the keys to the evolution of the epidemic. Instead of reasoning on abstract coefficients such as the famous average number R⁰ of contagions per person, we should be able to delve into the details of these contagions. We see here that traffic axes, institutions and housing probably occupy a strategic position towards an explanation.

This analysis is inevitably limited to the nature of the data and their possible faults. It would be useful to collect more detailed information on the nature of the contacts of each new case of contagion and to analyze it, or even to carry out random surveys with Covid-19 test, in a word, to make the statistics.

chain of lynx and drove of hares

Posted in Books, Kids, pictures, R, Statistics with tags , , , , , , , , , on February 27, 2020 by xi'an

A paper (and an introduction to the paper) in Nature this week seems to have made progress on the existence of indefinite predator-prey cyles. As in the lynx/hare dataset available on R. The paper is focusing on another pair, an invertebrate and its prey, an algae. For which the authors managed a 50 cycle sequence. What I do not get about this experiment is how the cycle can be tested via a rigorous statistical experiment.

“…the predator–prey system showed a strong tendency to return to the dominant dynamical regime with a defined phase relationship. A mathematical model suggests that stochasticity is probably responsible for the reversible shift from coherent to non-coherent oscillations, a notion that was supported by experiments with external forcing by pulsed nutrient supply.”

As I had not renewed my subscription to Nature in time, I could not check the additional material for details, but the modelling seems to involve a wavelet decomposition of the bivariate time series, with correlations between the two series…