In their summary there's a pretty massive gap in their lack of obtaining informed consent and how dangerous that might be:
"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."
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For those like me who lived under a rock, here's the study: http://www.pnas.org/content/early/2014/05/29/1320040111
In their summary there's a pretty massive gap in their lack of obtaining informed consent and how dangerous that might be:
"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."