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What Is Random Walk Theory & How it Works

The stock market uses various models and statistics to function. To effectively navigate this area, a proper knowledge of these models is required. A prominent model used is the random walk theory. This mathematical theory plays a vital role in assessing price movements. This article illustrates the critical information on random walk theory and its assumptions and provides information on its benefits and shortcomings. 

Defining random walk theory

To understand the usage of this model, it is essential to know what it is.

What is random walk theory?

A mathematics based model of the stock market is known as the Random Walk Hypothesis or Random Walk Theory. The theory’s proponents say that a random walk describes how stock market prices change over time. A statistical phenomenon known as a “random walk” occurs when a variable travels seemingly at random with no clear trend. The name comes from the random movement of the security prices. It is said that using technical or fundamental analysis to forecast future price movements is pointless.

This model follows that traders can never beat the market average unless it is due to coincidental factors. According to proponents of the random walk theory, investing in a selection of stocks that represent the entire market is advised. One such example of this would be an index mutual fund or exchange-traded fund (ETF) based on one of the major stock market indexes, like the S&P 500 Index.

History of random walk theory

French mathematician Louise Bachelier initially proposed the idea of the random walk theory because he thought that share price fluctuations were erratic, like a drunk person’s walk. The phrase first appeared in Eugene Fama’s 1965 article “Random Walks In Stock Market Prices,” which was a less technical version of his Ph.D. It was made popular by Princeton University economics professor Burton Malkiel’s 1973 book A Random Walk Down Wall Street.

Nonetheless, the hypothesis gained notoriety because of the contributions of economist Burton Malkiel, who concurred that stock prices follow an entirely random course. Consequently, the possibility that a share price will rise or fall at any given moment is equally equal. He even contends that a blindfolded monkey might randomly choose a portfolio of equities that would perform as well as one that was expertly chosen.

Random walk theory assumptions

A hypothesis cannot be deemed feasible unless empirical data supports it. It can be verified by experimentation or other forms of observation. However, a few assumptions are made to make the process more streamlined, which makes the theory more test-worthy. The assumptions of random walk theory are:

  • According to the theory, stock market security prices move randomly. 
  • It also presumes that the price of one security moves independently of the price of another.

Illustrating random walk theory

Random walk theory examples can be found in different real-life events. First, take stock and share price fluctuations into account. To predict future price changes, traders and investors continuously examine a variety of data sources, including news stories, earnings, dividends, and historical performance. However, since these price trajectories are unpredictable, the Random Walk Theory’s assumption precludes the possibility of gaining such an edge. 

Take a look at a game of roulette as an example. Each spin’s result would be unaffected by the results of earlier spins if you were to wager on red or black. This is similar to the Random Walk Theory’s description of the stock market, in which the next price movement’s direction is random and independent.

Random walk theory of consumption

Robert Hall is an economist who introduced the random walk model of consumption. This model uses the Euler numerical approach to simulate consumption. According to his theory, current income is the total of both permanent and transitory income. Since permanent income is the primary source of consumption, any fluctuations in consumption should be unpredictable. 

This means that if consumers have reasonable expectations, they should resemble a random walk. The random walk theory of consumption is examined after considering time accumulation prejudice. Because consumers only adjust their consumption in response to information about their lifetime resources, this model suggests that changes in consumption are unexpected.

Random walk theory and investing

The implications of random walk theory in portfolio management are significant and have shaped modern investment practices. It highlights how ineffective it is to try to beat the market just by timing the market or choosing stocks. Passive investment strategies have gained popularity as a result of this approach, in which investors aim to match market returns rather than exceed them. 

A long-term outlook is essential for successful investing, and diversification is critical for risk management. By encouraging investors to adopt disciplined portfolio strategies and cautious risk management, the random walk theory highlights the need to comprehend and accept market randomness.

Examining the benefits and shortcomings of random walk theory

There are several advantages and disadvantages of the random walk theory, as listed below. 


  • Efficient market insights: The random walk theory supports the efficient market hypothesis, which holds that stock prices accurately reflect all available information. This knowledge directs investors towards passive investing methods that seek to catch market returns rather than outpace them. 
  • Risk management: Investors are urged to concentrate on diversification and risk management by recognising the unpredictability of individual stock price fluctuations. Diversification among assets, industries, and regions lessens the effect that the performance of any one security has on the portfolio as a whole. 
  • Long-term view: The random walk hypothesis discourages investors from responding to transient market swings by emphasising a long-term investing view. This viewpoint is consistent with enduring short-term volatility while remaining dedicated to a well-considered investing strategy.


  • Market flaws: According to critics, the random walk theory ignores several anomalies and inefficiencies in the market that astute investors might exploit to earn higher returns. Behavioural biases, informational asymmetries, and market frictions can cause price variations that deviate from random fluctuations. 
  • Difficulties with active management: Random walk theory casts doubt on the efficacy of active portfolio management by implying that it is hard to outperform the market regularly. This could put off proactive investors who think they can spot cheap stocks or predict market trends. 
  • Limited predictive power: Technical analysis and other price-based forecasting methods are less effective because the theory claims that future price movements cannot be predicted solely by looking at past prices.


To sum up, random walk theory provides a basic foundation for comprehending stock price behaviour and how it affects investment methods. In order to overcome market unpredictability and meet investment goals, the random walk theory instead promotes passive investing techniques, diversification, and a lengthy investment horizon. Although some detractors may question their underlying assumptions and ignore specific market oddities, random walk theory continues to be a fundamental component of contemporary portfolio theory, directing investors towards responsible risk management and disciplined investing techniques.


Who developed the theory of random walks? 

French mathematician Louise Bachelier is credited with creating the random walk theory. However, economist Burton Malkiel’s work helped popularise it.

What effects does the random walk theory have on investment approaches?

The notion of random walks has important ramifications for investment approaches. It backs passive investing techniques, in which investors use diversified portfolios or index investing to try to match market returns. 

What arguments exist for the random walk theory?

The random walk theory has detractors who claim it simplifies market dynamics too much. It ignores some oddities and inefficiencies that astute investors might take advantage of for higher profits. They cite evidence of market anomalies, such as value investing techniques or momentum, to support their claims that short-term market behaviour is not totally random and efficient. 

Which aspects of the random walk theory are crucial? 

The Random Walk Theory assumes that prices are uniformly distributed, statistically independent, and unaffected by one another in efficient markets. Additionally, it assumes that investors will react logically to fresh information.

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