Looking at the details [1], it seems to be a small (N=180, then N=152) correlational study. How can we tell whether the effect is causal? One way would be to

Looking at the details [1], it seems to be a small (N=180, then N=152) correlational study. How can we tell whether the effect is causal? One way would be to run a randomized controlled trial, where you show some people slightly happier or sadder Facebook streams and you see how they react. This experiment has, in fact been run, [2] and what they found was that seeing happy status updates seemed to make people happier, not sadder. [3] [1] http://guilfordjournals.com/doi/abs/10.1521/jscp.2014.33.8.701 http://guilfordjournals.com/doi/abs/10.1521/jscp.2014.33.8.7... [2] http://www.pnas.org/content/111/24/8788.full http://www.pnas.org/content/111/24/8788.full [3] Though what they actually measured was what people posted, not their happiness. Perhaps seeing happy things leads you to be sad but post happy things to fit in.