Weak-form efficient market hypothesis

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Weak-form of market efficiency states that current market prices fully reflect all past market data.  This implies that investors cannot predict future price changes by extrapolating prices or patterns of prices from the past.  In other words,  technical analysis, which are strategies used to earn positive risk-adjusted returns by using historical price and volume data, cannot work in such a market.

Compare: Semi-strong-form efficient market, Strong-form efficient market