from the site:
The map is based on results from a study of geotagged tweets published earlier this year in PLoS ONE by researchers at the University of Vermont. The team scored more than 10,000 words on a positive-negative scale and measured their frequency in millions of tweets across the country, deliberately ignoring context to eliminate experimental bias. What emerged was significant regional variation in happiness by this calculation, which correlates with other lifestyle measures such as gun violence, obesity and Gallup's traditional wellbeing survey. A sadness belt across the South includes states that have high levels of poverty and the shortest life expectancies.