For millions of people, Twitter is not a happy place, according to a new study.
A survey by researchers at the University of Vermont examined 46 billion words written by 63 million people on the San Francisco-based micro-blogging site from around the world.
The study examined the "happiness level" of words tweeted out. Each word was given a different happiness grades, the higher the grade, the happier the word.
Volunteers helping on the study rated the 10,000 most commonly used words on Twiter under the method known as the Mechanical Turk.
Words such as "laughter" were given an 8.5 happiness rating while a word, such as "terrorist," received a 1.3.
Based on the rating system, the study found that Twitter users have become less happy over the past few years.
Also the fact that each tweet is time stamped and dated allowed the group to track certain happiness patterns.
It found that users were most unhappy in the first half of 2011.
