Psychohistory is a fictional science in the Asimov “Foundations” trilogy/universe.
Psychohistorians use certain algorithms and equations to accurately predict the actions of a large collective group of people / society.
A machine called the The Prime Radiant stores and processes the phychohistorical equations. The Psychohistorians use the information to shape the direction of social change.
On September 25, 1987, Asimov gave an interview to Terry Gross on her National Public Radio program, Fresh Air. In it, Gross asked him about psychohistory:
Gross: “What did you have in mind when you coined the term and the concept?”
Asimov: “[My editor] wanted an open-ended series so it lasts forever, perhaps. And so I started doing that. In order to keep the story going from story to story, I was essentially writing future history, and I had to make it sufficiently different from modern history to give it that science fictional touch. And so I assumed that the time would come when there would be a science in which things could be predicted on a probabilistic or statistical basis.”
Gross: “Do you think that would be good if there really was such a science?”
Asimov: “Well, I can’t help but think it would be good, except that in my stories, I always have opposing views. In other words, people argue all possible… all possible… ways of looking at psychohistory and deciding whether it is good or bad. So you can’t really tell. I happen to feel sort of on the optimistic side. I think if we can somehow get across some of the problems that face us now, humanity has a glorious future, and that if we could use the tenets of psychohistory to guide ourselves we might avoid a great many troubles. But on the other hand, it might create troubles. It’s impossible to tell in advance.”