Losada's article was critiqued by Andrés Navas in a Note to the French website of the CNRS "Images des Mathématiques". The whole theory of the critical positivity ratio was strongly critiqued by Nicholas Brown, Alan Sokal, and Harris Friedman, in a 2013 article published in "American Psychologist". Brown et al. argue that Losada's conclusions in previous papers using modelling from fluid dynamics, and those in his paper co-authored with Fredrickson, are not only based on poorly reported experiments – they argue that it is difficult to draw any conclusions from some previous studies by Losada because critical details are omitted, and "interpretations of results are made with little or no justification" (p. 5) – but are based on elementary errors in the use of differential equations.