Reseachers claim ‘universal’ positivity bias in human language

“Human language reveals a universal positivity bias” claims a large scale research study…

“The most commonly used words of 24 corpora [word collections] across 10 diverse human languages exhibit a clear positive bias [toward use of words with positive meanings]”

The researcher’s word collections came from places such as: Google Books; Google Web crawls; movie and television subtitles; the New York Times; music lyrics; and Twitter. The most frequent words in those collections were then ranked by 5 million individual scores, which means the researchers paid native speakers to rank them.

The authors don’t appears to detail the demographics of the people they paid to rank the words. If they were all undergraduates, I wonder if there may have been a positivity bias induced by the youth of the rankers?