Significance
We show, via a massive (N = 689,003) experiment on Facebook, that emotional states can be transferred to others via emotional contagion, leading people to experience the same emotions without their awareness. We provide experimental evidence that emotional contagion occurs without direct interaction between people (exposure to a friend expressing an emotion is sufficient), and in the complete absence of nonverbal cues. PNAS
Abstract
Emotional states can be transferred to others via emotional contagion, leading people to experience the same emotions without their awareness. Emotional contagion is well established in laboratory experiments, with people transferring positive and negative emotions to others. In an experiment with people who use Facebook, we test whether emotional contagion occurs outside of in-person interaction between individuals by reducing the amount of emotional content in the News Feed. When positive expressions were reduced, people produced fewer positive posts and more negative posts; when negative expressions were reduced, the opposite pattern occurred. These results indicate that emotions expressed by others on Facebook influence our own emotions, constituting experimental evidence for massive-scale contagion via social networks. PNAS
Experiment (summary from the paper)
The experiment manipulated the extent to which people (N = 689,003) were exposed to emotional expressions in their News Feed. Two parallel experiments were conducted for positive and negative emotion: one in which exposure to friends’ positive emotional content in their News Feed was reduced, and one in which exposure to negative emotional content in their News Feed was reduced. Posts were determined to be positive or negative if they contained at least one positive or negative word, as defined by Linguistic Inquiry and Word Count software (LIWC2007). Both experiments had a control condition, in which a similar proportion of posts in their News Feed were omitted entirely at random. Participants were randomly selected based on their User ID, resulting in a total of ~155,000 participants per condition who posted at least one status update during the experimental period. PNAS
Fig. 1: Mean number of positive (Upper) and negative (Lower) emotion words (percent) generated by people, by condition. PNAS
Key results (from the paper)
When positive posts were reduced in the News Feed, the percentage of positive words in people’s status updates decreased by B = −0.1% compared with control, whereas the percentage of words that were negative increased by B = 0.04%. Conversely, when negative posts were reduced, the percent of words that were negative decreased by B = −0.07% and the percentage of words that were positive increased by B = 0.06%. The authors note effect sizes are small but argue that small effects can have large aggregated consequences at massive scale. PNAS
Public reaction and ethics (reporting)
Protests followed after it emerged Facebook had conducted a psychology experiment on nearly 700,000 users without their knowledge, manipulating news feeds to control which emotional expressions users were exposed to. Activists, politicians and commentators described the mass experiment as “scandalous”, “spooky” and “disturbing” and raised concerns about informed consent, privacy and the power to influence thoughts and behaviour. A senior British MP called for a parliamentary investigation into how Facebook and other social networks manipulate emotional and psychological responses of users by editing information supplied to them. The Guardian
Facebook said the research was carried out “to improve our services and to make the content people see on Facebook as relevant and engaging as possible” and noted the work was consistent with Facebook’s Data Use Policy; one of the study’s authors said they were “very sorry for the way the paper described the research and any anxiety it caused.” Critics said participants should have been told they were taking part in research and given the chance to consent. BBC The Guardian
Photograph: Dado Ruvic/Reuters. The Guardian
BBC
Short takeaway (from sources)
- Experimental evidence shows emotional expressions seen on social networks can influence subsequent emotional language used by users, even without direct interaction or nonverbal cues. PNAS
- The manipulation produced small effect sizes at the individual level but has potential for large aggregate impact at platform scale. PNAS
- The study generated substantial ethical debate about consent, privacy, and the responsibilities of platforms running large-scale experiments on users. The Guardian BBC
What’s Your Take?
- What impact could this kind of platform-level influence have locally or globally?
- Do you agree that the study’s results matter despite small individual effect sizes?
- How should policymakers and platforms balance product testing with informed consent and privacy?
- What lessons can researchers and engineers learn from the public reaction to improve ethics and transparency?