Yes, ECLECTICISM is a Scrabble word!

Letter values in Scrabble US: E 1, C 3, L 1, E 1, C 3, T 1, I 1, C 3, I 1, S 1, M 3.

Is it a valid word?

ECLECTICISM is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

making decisions on the basis of what seems best instead of following some single doctrine or style

Also: eclectic method.