The following article just appeared in the British Medical Journal: Vinkers CH, Tijdink JK, Otte WM. Use of positive and negative words in scientific PubMed abstracts between 1974 and 2014: retrospective analysis. BMJ 2015;351:h6467 Here is a related news item from the first author's institution, unfortunately in Dutch only. The publication was also mentioned in the Dutch popular press today. In any case, I wonder to what extent a similar phenomenon would also be visible in the contemporary physics and mathematics literature. (The authors only looked at publications in PubMed.) Perhaps the trend signalled in the article is due to the tendency of most scientists to be "excellent" these days.