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Random Walk Theory and Technical vs Fundamental Analysis under EMH

Updated 11 October 2026 · Fact-checked

Random walk theory says successive price changes are independent, so past prices cannot predict future prices. It follows from an efficient market, where new information is reflected quickly. Under weak form efficiency technical analysis fails; under semi-strong form fundamental analysis also fails to earn excess returns. Passive, diversified strategies then make sense.

Understand Random Walk Theory and Technical vs Fundamental Analysis

Start with a simple idea. A share price moves when new information arrives. News is, by nature, unpredictable. If it were predictable, it would already be in the price. So price changes themselves look unpredictable.

This is the random walk theory. It says that price changes are independent of earlier price changes and follow no usable pattern. Tomorrow's change cannot be forecast from today's or last month's change. It does not say prices are irrational or that prices never trend. It says the changes are unpredictable because they are driven by new information.

The link to the Efficient Market Hypothesis (EMH) is direct. If many informed investors compete and prices adjust quickly to new information, prices already reflect what is known. Only fresh news moves them, and fresh news is random. So an efficient market produces random price changes. Random price changes are evidence consistent with weak form efficiency.

Technical analysis studies past prices and volumes, using charts and indicators, to predict future prices. Fundamental analysis studies economic, industry and company data (earnings, growth, risk) to estimate intrinsic value and buy shares priced below it. The two rest on different beliefs. Technical analysis assumes patterns repeat. Fundamental analysis assumes price can differ from value for a while and then correct.

What EMH says about each depends on the form. In the weak form, prices reflect all past price data, so technical analysis cannot earn excess returns. In the semi-strong form, prices reflect all public information, so fundamental analysis using public data also fails. Only inside information could help, unless the strong form holds, in which even that fails. The practical result for investors: if markets are efficient, hold a well-diversified portfolio, keep costs and turnover low, and choose risk level to suit your needs rather than trying to beat the market.

Key rules to remember

Random walk (price change form): Pₜ = Pₜ₋₁ + expected return + random error (εₜ); The error term is unpredictable and uncorrelated with past errors. Correlation between successive price changes is close to zero.
Weak form efficiency: Prices reflect all past price and volume data; Technical analysis cannot give excess returns. Fundamental analysis and insider information might.
Semi-strong form efficiency: Prices reflect all publicly available information; Both technical and fundamental analysis of public data fail. Insider information may still help.
Strong form efficiency: Prices reflect all information, public and private; Even insiders cannot earn abnormal returns.
Abnormal return: Abnormal return = Actual return − Expected return (as per risk-return model); EMH says abnormal returns cannot be earned consistently after adjusting for risk and costs.

How to solve Random Walk Theory and Technical vs Fundamental Analysis questions

Use this method for theory questions, short cases and 'which form is violated' questions.

1Identify what information the strategy uses: past prices and volume, public data, or private data.
2Match that information to the form of efficiency: past prices to weak, public to semi-strong, private to strong.
3State what EMH predicts for that strategy: no consistent excess return after adjusting for risk and costs.
4If numbers are given, check whether the returns are abnormal by comparing actual with the expected return from the risk model, not with zero.
5Check whether the evidence is consistent with a random walk, for example near-zero correlation between successive price changes.
6Conclude which analysis, if any, can work, and name the form that must be false for it to work.
7Give the portfolio implication: diversify, keep costs low, avoid frequent trading, and consider passive funds.

Quickest way: Information-to-form matching

When to use it: Use for MCQs and short questions where you must decide whether an analysis can beat the market.

Ask: what information does the method use?
Past prices means weak form; public data means semi-strong; private data means strong.
A method works only if the market is not efficient in that form or a higher form.
So technical analysis needs weak form to be false. Public-data fundamental analysis needs semi-strong to be false. Insider trading needs strong form to be false.
Pick the option that states this chain.

Common mistakes in Random Walk Theory and Technical vs Fundamental Analysis

Saying random walk means prices are random or irrational.
The word 'random' is read literally.
Fix: Say that price changes are unpredictable because they respond to new information. Prices themselves reflect available information.
Saying EMH makes fundamental analysis useless for everyone.
Students stop at the semi-strong form.
Fix: Say that analysts' work is what makes prices efficient. EMH says it cannot earn consistent excess returns after costs once prices adjust.
Claiming technical analysis fails under all three forms and fundamental under only the strong.
Mixing up which information each form covers.
Fix: Weak form rules out technical analysis. Semi-strong rules out fundamental analysis on public data too. Strong rules out insider gains as well.
Treating a profitable trade as proof that markets are inefficient.
Ignoring luck and risk.
Fix: Judge returns after adjusting for risk and costs, and over many trades. A few gains can be chance.
Saying EMH implies no one should invest.
Confusing no excess return with no return.
Fix: Investors still earn the expected return for bearing risk. EMH only says there is no free extra return from analysis.
Ignoring portfolio implications in a 'discuss' answer.
Stopping at definitions.
Fix: Always end with the strategy: diversified, low-cost, passive, with asset allocation matched to risk tolerance.

Worked examples

Example 1

A trader in an Indian mid-cap stock finds that when the price rises 3% in a week, it rises again the next week in most cases, and she earns steady profits by buying after such rises. Which form of EMH does this contradict, and what does it say about technical analysis and the random walk theory?

Show the solution

The strategy uses only past price data (last week's price change).
Past price data is the information set of the weak form.
Steady profit from this rule means prices do not fully reflect past price information.
Successive price changes are positively related, so they are not independent. This goes against the random walk.
If the profit holds after risk adjustment and transaction costs, weak form efficiency, and therefore also semi-strong and strong forms, would be rejected.

Answer: The evidence contradicts weak form efficiency and the random walk. It would support technical analysis in this stock, provided profits persist after risk and costs. A short run of gains alone is not proof.

Example 2

An analyst studies a company's published annual results and values a share at ₹480 against a market price of ₹400. She buys on the day results are published and earns a return no higher than the market after adjusting for risk. Explain what this suggests under EMH and what it means for portfolio strategy.

Show the solution

The analyst uses published results, which are public information.
Public information relates to the semi-strong form.
Her risk-adjusted return is no higher than the market, so there is no abnormal return.
This is consistent with semi-strong efficiency: the price had already adjusted to the results by the time she could trade.
Technical analysis would also fail, since the weak form is implied by the semi-strong form.
Strategy: avoid costly active trading on public data. Hold a diversified portfolio, possibly an index fund, and set the risk level by the investor's needs.

Answer: The result is consistent with semi-strong efficiency. Fundamental analysis of public data gave no excess return. The investor should follow a diversified, low-cost, largely passive strategy.

Exam tips

Write the link in one line: efficient market, so prices reflect information, so changes are driven by news, so they follow a random walk.
In comparison questions, use two columns in your mind: input data, method, belief, and EMH verdict for each analysis.
For case MCQs, find the information used first and then name the form. Do not start from the profit.
In long answers, end with the implications for investors: diversification, low cost, passive funds, and the role of analysts in keeping prices efficient.
Do not claim EMH is proven or disproven. Say evidence is mixed and anomalies exist.

Practice questions from Efficient Market Hypothesis

Random Walk Theory and Technical vs Fundamental Analysis in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Random Walk Theory and Technical vs Fundamental Analysis: frequently asked questions

How is random walk theory related to EMH?

Random walk theory describes the behaviour of price changes: they are independent and unpredictable. EMH explains why: prices already reflect available information, so only new information moves them. Random price changes are therefore consistent with an efficient market.

Can technical analysis work in an efficient market?

Under weak form efficiency, no. Past prices and volumes are already in the price, so patterns give no consistent excess return after costs. If technical analysis does earn abnormal returns, it indicates the market is not weak form efficient.

What is the difference between technical and fundamental analysis in the EMH context?

Technical analysis uses past prices and volume to predict the next move. Fundamental analysis uses economic, industry and company data to estimate intrinsic value. Weak form efficiency challenges the first. Semi-strong form challenges both when based on public data.

What are the implications of EMH for investors?

Investors cannot expect to beat the market consistently by analysis alone. A diversified, low-cost portfolio with low turnover is sensible, and asset allocation should match risk tolerance. Active management is justified only if the market is not efficient.