Forty six billion tweets don't lie: We're collectively getting more depressed. Or at least those of us on Twitter are, judging from our use of sad words like "greed," "terrorist," and "suicide." We've been in a depression spiral since April 2009, according to science. How dismal!

A University of Vermont team led by an applied mathematician conducted a survey to assign a "happiness" score to certain keywords. Then, for three years, they used these scores to analyze the joviality of tens of millions of Twitter users. The result? Well, it's graphed here, and here's how the research team summarized it:

"After a gradual upward trend that ran from January to April, 2009, the overall time series has shown a gradual downward trend, accelerating somewhat over the first half of 2011... It appears that happiness is going down."

So you're not the only one who started self medicating after the financial collapse - or who upped his dosage this year. Of course, it's worth noting that the research team includes a physicist, computer scientist, and "complex systems" scholar, but not one psychologist. Did anyone think to control for the fact that the subjects just got more and more unhappy as they spent more and more time on Twitter?

[via Psych Central]

[Image via Yuri Arcurs/Shutterstock and PLoS]