It is well established that humans across languages and cultures have a tendency to use more positive words than negative ones. This is called linguistic positivity bias (LPB), but why the phenomenon exists remains unclear. Now researchers report in the Proceedings of the National Academy of Sciences that their big data analysis of 200 years of words in Google Books (1.3 million texts from 1800 to 2000) and New York Times archives (14.9 million articles since 1851) suggests that the ratio of positive to negative written words "correlates strongly" with the Misery Index (which measure economic health) and war casualties. They also found that LPB has been on the decline, with researcher Morteza Dehghani calling it, "very generally, an indicator that happiness may be on the decline in the US."
But outside scientists urge caution when interpreting the results. The New York Times says the study does offer up evidence that objective circumstances (like war deaths and the economy, as noted above) and subjective happiness can alter our language, there are confounding factors at play in terms of citing a centuries-long decline. UPenn linguistics prof Mark Liberman, for instance, takes issue with the database of 907 words run against the texts, and give the example of "awesome," which has evolved from meaning "daunting" to "excellent." The researchers acknowledge that "our results ... encourage the development of more precise tools for inferring psychological states from historical texts." (Even the final words of death row inmates tend to be positive.)