[gammarator]

That's what I said: A/B tests improve the site "in aggregate."

The goal of this study was not to improve the site, though: it was to test a hypothesis about social psychology.

[yincrash]

The goal of the study _is_ to improve the site. Facebook wants the users to return to the site, and users who become happier when using the site do that. Facebook isn't paying its data scientists to perform studies that have no meaningful use.

[akerl_]

I sincerely hope you're not making the case that testing a hypothesis for a scientific paper is not a valid reason to perform such an experiment, but improving a website is.