Facebook has considered profiling its users' personalities and using the information to target adverts.
A patent filed by the social network describes how personality characteristics, including emotional stability, could be determined from people's messages and status updates.
The firm is currently embroiled in a privacy scandal over the use of its data by a political consultancy.
Facebook says it has never used the personality test in its products.
The patent, first filed in 2012, is in the names of Michael Nowak and Dean Eckles.
Mr Nowak has worked for Facebook for 10 years, while Prof Eckles now teaches at the Massachusetts Institute of Technology.
The patent has been updated twice, most recently in 2016.
(culled from BBC)
