random walk theory
The theory that stock price changes are random and unpredictable, making technical analysis and market timing futile because past prices don't predict future prices.
Example
“Random walk theory suggests a blindfolded dart-throwing monkey would match a professional stock picker's performance over time.”
Memory Tip
RANDOM WALK = tomorrow's price is random relative to today's. Past prices don't help predict future.
Why It Matters
Understanding random walk theory helps you avoid wasting money on expensive investment advisory services and trading strategies that claim to beat the market. It suggests that the best approach for most people is to invest in low-cost index funds rather than trying to time the market or pick individual stocks based on past performance.
Common Misconception
Many people believe that if a stock has gone up for several days in a row, it is more likely to continue rising, or that studying historical price charts can reveal predictable patterns. Random walk theory shows this is false because past price movements have no bearing on future prices, and patterns are often just coincidence.
In Practice
Imagine you notice that a company stock rose 5 percent each month for the last three months and you decide to buy it expecting the trend to continue. Random walk theory suggests this past performance tells you nothing about whether the stock will rise or fall next month, so your decision is based on an illusion rather than genuine predictive information.
Etymology
RANDOM WALK (a path determined by random steps) THEORY. Stock prices move like a RANDOM WALK — each step unpredictable.
Common Misspellings
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