Financial Management · Nature and purpose of the valuation of business and financial assets

Efficient Market Hypothesis and Valuation for ACCA FM

Updated 11 October 2026 · Fact-checked

The efficient market hypothesis (EMH) says share prices fully reflect available information, so prices change only when new information arrives. There are three forms: weak (past prices), semi-strong (all public information) and strong (public and private information). To answer questions, match the information in the scenario to the form it tests.

Understand Efficient Market Hypothesis and Valuation

A market is efficient if share prices quickly and fully reflect the information available. If that is true, a share's price is a fair estimate of its value. You cannot reliably beat the market by studying information that is already priced in.

Prices move when new information arrives. New information is unpredictable, so price changes are random. This is called a random walk. Random does not mean irrational. It means you cannot predict the next move from what you already know.

The three forms depend on which information is priced in:

Weak form: prices reflect all past price and trading data. Studying charts (technical analysis) cannot give abnormal returns.
Semi-strong form: prices reflect all publicly available information. This includes past prices, accounts, announcements and news. Fundamental analysis of public data cannot give abnormal returns.
Strong form: prices reflect all information, including private or insider information. Even insiders cannot make abnormal gains.

Each form includes the one before it. If a market is semi-strong efficient, it is also weak form efficient.

The evidence is mixed. Studies of past price patterns generally support weak form. Studies of how prices react quickly to announcements, such as results or takeover bids, generally support semi-strong form. Strong form is usually rejected, because insider dealing can earn gains, which is why it is illegal. Evidence against efficiency includes bubbles and crashes, calendar effects, overreaction to news, and investors who do not act rationally.

For a financial manager, the key point is that if the market is at least semi-strong efficient, the share price is a fair reflection of value. Managers cannot fool the market with cosmetic accounting changes, and the market will react to genuine news about future cash flows.

Key rules to remember

Weak form efficiency: Price = reflects all past price and trading data; Charts and past price patterns give no abnormal return. Tests: no pattern in price changes.
Semi-strong form efficiency: Price = reflects all public information; Includes weak form. Only private information can help. Tests: prices adjust quickly to announcements.
Strong form efficiency: Price = reflects all public and private information; Includes semi-strong. Insiders cannot gain. Evidence generally rejects this form.
Abnormal return: Abnormal return = actual return − expected return for the risk taken; Used to test efficiency. In an efficient market, only new information causes abnormal returns.

How to solve Efficient Market Hypothesis and Valuation questions

Use this method for any EMH question, whether objective test or written.

1Read the scenario and list what information the investor or manager is using, such as past prices, published accounts or inside knowledge.
2Match that information to a form: past prices means weak, public information means semi-strong, private information means strong.
3Remember the forms are cumulative, so a stronger form implies all the weaker ones.
4Decide what the form implies: if the information is already priced in, using it cannot give abnormal returns.
5If asked for evidence, state what supports or contradicts the form, and say what the evidence suggests about real markets.
6If asked for implications, link to the manager: share price is a fair value, timing of issues is pointless, disclosure matters, and managers cannot mislead the market.
7Finish with a clear conclusion that answers the exact question asked.

Quickest way: Match the information to the form

When to use it: Section A and Section B objective questions that ask which form is being tested or which strategy would fail.

Underline the information used in the question.
Past prices only: weak form. Published or public data: semi-strong. Insider information: strong.
Pick the weakest form that covers the information. A strategy using public data fails if the market is semi-strong or strong, but may work in a weak-form-only market.
Check wording such as 'at least' or 'only'. Then choose the answer.

Common mistakes in Efficient Market Hypothesis and Valuation

Saying weak form means prices are random or wrong.
Students confuse random price changes with irrational prices.
Fix: State that prices reflect information and change only on new information, which is unpredictable.
Mixing up which information belongs to which form.
The names are not descriptive and students memorise them poorly.
Fix: Link them: weak = past prices, semi-strong = public, strong = private as well. Each includes the previous one.
Claiming that strong form efficiency is supported by evidence.
Students assume efficient markets means everything is priced in.
Fix: Say that evidence generally rejects strong form, since insiders can earn abnormal gains.
Saying efficient markets mean shares are never mispriced or that nobody can ever make a profit.
Overstating the theory.
Fix: Say investors earn a return for risk, but cannot reliably earn abnormal returns from information already in the price.
Giving implications for managers that are generic rather than linked to EMH.
Students write about shareholder wealth in general.
Fix: Use specific points: price is a fair value, timing share issues is pointless, cosmetic accounting changes do not fool the market, and clear disclosure reduces uncertainty.

Worked examples

Example 1

An analyst makes profits by studying published financial statements and finding companies whose reported earnings are higher than the market expects. She finds she consistently earns abnormal returns. Which form of efficiency does this evidence reject, and what does it say about the other forms?

Show the solution

The information used is published financial statements, which is public information.
Public information is tested by semi-strong form.
If abnormal returns are consistently earned from public information, the market is not semi-strong efficient.
Strong form includes semi-strong, so strong form is also rejected.
Nothing is shown about weak form. The analyst uses accounts, not past price patterns, so weak form could still hold.

Answer: The evidence rejects semi-strong form, and therefore strong form too. It does not by itself reject weak form.

Example 2

The finance director of a listed company proposes delaying the announcement of a rights issue until the share price rises, and changing the inventory valuation method to increase reported profit. Explain whether this is sensible if the market is semi-strong form efficient.

Show the solution

In a semi-strong efficient market, the price reflects all public information and changes only when new information arrives.
Timing the issue: future price movements are unpredictable, so waiting for a rise has no expected benefit. The price is a fair value now.
Changing inventory valuation: this alters reported profit but not cash flows. The market can see the policy change in the public accounts and adjust for it.
So the higher profit will not increase the share price. If cash flows are unchanged, value is unchanged.
The sensible action is to base the decision on whether the issue funds positive NPV projects, and to disclose clearly.

Answer: Neither action is sensible. The price is a fair reflection of value, so timing the issue gives no expected gain, and a cosmetic accounting change will be seen through by the market because it does not change cash flows.

Exam tips

In objective questions, find the information used first. It decides the form.
Remember that forms are cumulative. A semi-strong market is also weak-form efficient.
In written answers, give evidence for and against, then conclude that real markets are broadly semi-strong efficient but not perfectly so.
For implications questions, give three or four distinct points and tie each to the financial manager's decisions.
Do not claim that efficiency means prices are always correct. Say prices reflect available information.

Practice questions from Nature and purpose of the valuation of business and financial assets

Efficient Market Hypothesis and Valuation in other exams

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

Efficient Market Hypothesis and Valuation: frequently asked questions

What is the difference between weak, semi-strong and strong form efficiency?

The difference is the information that is already reflected in the share price. Weak form covers past prices, semi-strong covers all public information, and strong form covers public and private information. Each form includes the ones before it.

What are the implications of the EMH for financial managers?

The share price is a fair estimate of value, so managers should focus on positive NPV projects. Timing share issues to catch a high price does not work, and cosmetic accounting changes do not fool the market. Clear and honest disclosure helps the market value the company properly.

What is the evidence for and against efficient markets?

Evidence for includes the lack of predictable patterns in past prices and the quick reaction of prices to announcements. Evidence against includes bubbles and crashes, overreaction to news, calendar effects and gains from insider information. Most evidence supports weak and semi-strong form but not strong form.

How is the EMH tested in ACCA FM?

It appears in objective questions that ask you to match a scenario to a form, and in written parts that ask for evidence or implications. Read the information used and match it to the form. Then apply what that form implies.