Good tweeting is often an exercise in good editing — cramming any thought into 140 characters can be a challenge in itself, let alone coming up with something smart or witty. But it turns out that a lot of us have actually become pretty effective at not hitting the character limit. The MIT Technology Review relays this chart from researchers at the University of the Philippines:

What you're seeing is a subset of 229 million tweets gathered from four years of Twitter usage. The researchers tallied up the number of words in each tweet and correlated them by the year they were published. The chart above represents all the tweets that were sampled on the first Friday in December of a given year. Over time, the results show an initial increase in the average tweet length, followed by a rapid decline.

In 2009, the share of tweets numbering 40 characters or fewer was pretty balanced against the proportion of tweets numbering 120 characters or more. The following year saw a spike in the proportion of tweets numbering around 120 characters. But ever since then, tweets have been getting shorter and shorter — to the point that long tweets now account for only a tiny fraction of all tweets.

The researchers suggest that the rise of jargon and other linguistic conventions on the service could be behind the trend. It's a plausible theory, particularly as more people begin writing with tweets in mind more generally. My own pet theory? Blame the pornbots.