As Sir Isaac Newton said in his First Law of Motion: An object in motion will stay in motion, unless an outside force acts upon it.
That gave rise to the concept of momentum. In the financial markets, price has momentum too. Daryl Guppy, documented in his book about the characteristics of price movement of shares. He verified his obervations with actual results and here are the details:
A stock trading within a band (price range) has a 70% chance to move sideways further. This leaves 50% chance to either move up or down. Hence, there is a 15% chance to go up and a 15% to go down.
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When the stock price is moving up, there is a 75% chance for it to move in the same direction, and within the price channel. Unlike the sideway price action, probability to accelerate up and down are no longer equal. There is a higher chance for the price to accelerate upwards at 15% and a lower tendency to accelerate downwards, which was found to be 10%. Quoting Daryl, “pick a stock like this and the balance of probability is overwhelming on your side.”
When the stock is trending down, there is a 80% probability for the stock to continue in the same direction. It also has a 15% for the stock to accelerate downwards while it only has a 5% chance for it to accerlerate upwards.