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FinanceEfficient Market Hypothesis (EMH)
By Sitraka Forler · Lecturer, Durham Business SchoolUpdated 13 September 2026 About this site
Prices already reflect all available information.
In its weak/semi-strong/strong forms, EMH argues you cannot consistently beat the market because new information is instantly priced in. It justifies index investing and sets the bar that any alpha-seeking strategy must clear after costs.