“Bipolar (Disorder) people must have magnets to one another, because since I met you I have met all your friends and they all have Bipolar Disorder,” observes my partner. So I do a quick search of the internet:
A 2009 thread describes a similar phenomenon. In fact, most of the “evidence” I found was anecdotal (about 8 forums that spanned 2009-2015).
However, social psychology holds the following basic tenant: