It was so inconspicuous you could have missed it, particularly if you rarely post Facebook status updates or comb your newsfeed. It was such a minor change that even the most diehard users would not have taken notice.
But now the word is out: in early 2012, almost 700,000 users were randomly selected for a Facebook psychological experiment. The premise was simple. Facebook set out to alter the number of positive or negative posts users saw in their newsfeeds to see what effect this change had on the tone of the posts the recipients then wrote in their own status bars. Perhaps as one might expect, researchers found that moods were contagious: those who were inundated with a series of optimistic posts responded by sharing positivity of their own in their statuses while those who were saturated with negativity expressed the same dejection in their own posts.