Before revision: As established by Birger Wernerfelt and Aneel Karnani in their article "Competitive Strategy Under Uncertainty", "Competitive Strategy Under Uncertainty" there are four different kinds of sources: demand structure, supply structure, competitors and externalities.
After revision: As established by Birger Wernerfelt and Aneel Karnani in their article , "Competitive Strategy Under Uncertainty" there are four different kinds of sources: demand structure, supply structure, competitors and externalities.