Actually, it hardly proves anything

I'm not much of a statistics person, but it seems to me that we're dealing with a pretty minor effect. From the text of the study it appears that negative or positive status updates do influence the updates that those who receive them post:

The results show emotional contagion. As Fig. 1 illustrates, for people who had positive content reduced in their News Feed, a larger percentage of words in people’s status updates were negative and a smaller percentage were positive. When negativity was reduced, the opposite pattern occurred. These results suggest that the emotions expressed by friends, via online social networks, influence our own moods, constituting, to our knowledge, the first experimental evidence for massive-scale emotional contagion via social networks (3, 7, 8), and providing support for previously contested claims that emotions spread via contagion through a network.
If we read those sentences without viewing Fig. 1 that's pretty much a logical conclusion. The problem is that when we view the chart itself, we realize that we're dealing with a very minimal influence. As Tal Yarkoni notes:
these effects, while highly statistically significant, are tiny. The largest effect size reported had a Cohen’s d of 0.02–meaning that eliminating a substantial proportion of emotional content from a user’s feed had the monumental effect of shifting that user’s own emotional word use by two hundredths of a standard deviation. In other words, the manipulation had a negligible real-world impact on users’ behavior. To put it in intuitive terms, the effect of condition in the Facebook study is roughly comparable to a hypothetical treatment that increased the average height of the male population in the United States by about one twentieth of an inch (given a standard deviation of ~2.8 inches). Theoretically interesting, perhaps, but not very meaningful in practice.
It's hard not to get the impression that our willingness, and in this case perhaps even our enthusiasm, to believe anything about Facebook has caused too many people to see these results, and the experiment as a whole, as much more significant that it really was.


Go to: What isn't an experiment?