Sociology
History
Statistics
Calculus(all forms)
Chaos Theory
Systems Theory
Systems Engineering
Psychology
Political Anthropology
Game Theory
Statistical Mechanics
Sociophysics

Please add more if you can.
P.S
I recommend reading "A Beautiful Math" By Tom
Siegfied
P.P.S
Is this place still alive?
-Regards,
Psychology Lover

Large scale psycho-historical analysis definitely cannot be done without the use of computers, so I would add computer science to that.

Ah yes I completely forgot to add that. Thank you for your contribution!
-Psychology Lover

This website (below) has numerous ideas which may be valuable to psychohistory, such as how Bruce Bueno de Mesquita has predicted successfully and scientifically the political movements in Iran during February 2009.
The article also mentions that Indiana University has tracked the movements of 100,000 people over a 6 month period. Indiana University researcher Alessandro Vespignani believes he will one day be able to predict large scale pandemcics.

nextbigfuture.com . . .

-Psychology Lover

I understand the idea, but what was the actual computer model he used to make predictions? A really neat idea in the article was tying down the key decision maker with people who influence him or her and breaking down these influences based on their agenda and power. Could be a great tool for predicting policy making.