No, emotions aren’t really contagious over Facebook

You’ve probably heard the news: Facebook and Cornell University teamed up to manipulate your Facebook feed and toy with your emotions. The results, published in a high-tier academic journal, sparked heated debates across media platforms as the study did not include any prior consent or post-study debriefing.

Aside from the precarious ethics, what else can we gleam from the study? (Not much.)

The study looked at ‘emotional contagion’, a phenomenon whereby people subconsciously take on the emotional states of others they interact with, often in a laboratory setting. To see if it occurs in the real-word through online social networks, researchers tweaked the Facebook news feeds of 689,003 users (~155,000 per condition) for a week and monitored their subsequent status updates for emotional expression. Specifically, an algorithm searched for posts containing at least one word that expresses either positive or negative emotions, and then omitted those posts 10-90% of the time from viewers. Matched controls had a similar percentage of random posts withdrawn from their feeds.

Through statistical modelling, the researchers found that when positive posts were omitted, the viewers’ subsequent status updates contained a larger percentage of negative words compared to controls. How much larger? 0.04%. Conversely, when negativity was reduced from the feeds, the percentage of positive words in later posts increased by 0.06%. The results were highly statistically significant.

The authors thus concluded that our friends’ emotions impact our own moods through online social networks. But does it really? The influences are minute – only a fraction of a percentage – and the main reason they were detected at all is because of the extraordinarily large sample size. And herein lies an important distinction in research: statistically significant versus actually relevant. In this case, your friend’s flaming post on Facebook might make you angry (because the stats did find a link), but its impact is so small it could easily be overridden by other factors in your life. A study from 2011, for example, concluded that reading your Facebook's friends chipper updates made you feel inferior and miserable.

To the authors’ credit, they openly admitted this effect size issue in their discussion, but then argued that the effects are not negligible at Facebook's scale. Whether they are relevant for real life, however, remains to be seen.

Kramer AD, Guillory JE, & Hancock JT (2014). Experimental evidence of massive-scale emotional contagion through social networks. Proceedings of the National Academy of Sciences of the United States of America, 111 (24), 8788-90 PMID: 24889601