Does the Existence of Predictable Price Patterns Contradict the Weak Form of EMH?

Yes, the existence of consistently profitable, predictable price patterns contradicts the Weak form of EMH. Weak form efficiency states that past prices and volume data cannot be used to predict future prices in a way that yields abnormal returns.

If a pattern, such as a specific chart formation, reliably leads to profit after accounting for transaction costs, it suggests the market is not fully Weak-form efficient. Arbitrageurs would quickly eliminate such patterns.