The paper under discussion is a very well-written and interesting piece of work by Secchi et al. (2015) dealing with spatio-temporal data on mobile phone use in the area of Milan. I congratulate the authors for such a stimulating and interesting paper. It clearly points out that Erlang data on mobile phone use contain a large amount of rich information. The paper is an excellent example of statistical analysis of Big Data. I discuss briefly two alternative ways of dimension reduction of spatio-temporal data and illustrate them with artificial data that has been simulated according to the scheme proposed by the authors.
CitacióDelicado, P. Discussion of “Analysis of spatio-temporal mobile phone data: a case study in the metropolitan area of Milan” by Piercesare Secchi, Simone Vantini and Valeria Vitelli. "Statistical Methods and Applications", 21 Maig 2015, vol. 24, núm. 2, p. 329-333.