What determines ranked pick order?

I think it's random when you queue up alone. Queuing up as a 5-man has some bias, I believe, however.

i hate this personally i wish we could swap pick order.. i HATE being first pick as my champ is never picked or banned but is REALLY easy to counterpick. at the same time most of my teammates want the OP shit, and i don't own my "non op champs"

Im generally first pick in majority of my games and i play mostly solo. This is across Norms draft and ranked draft (both Ques) i dont know if its random and im unlucky or the game just hates me. I thought it was because i play top alot but even with other roles im just generally first pick.

Is it based on party leader, position, MMR? Has riot ever clarified?