A study where scientists from the University of Vermont analyzed word content of 4 billion tweets posted by 63 million Twitter users worldwide over a span of three years revealed that users of the microblogging site may be less happy now than they used to be.

The tweets went out between September 2008 and mid-September 2011, offering almost an instant look over the “collective shoulder of society” in near-real time, according to researcher Peter Dodds, PhD at the college of engineering and mathematical sciences at the University of Vermont in Burlington. The research was published online in the journal PLoS ONE.