Market efficiency differs across markets, countries, and securities.
Large and liquid markets are usually more efficient because they have more participants, better disclosure, and lower trading costs. Smaller or less developed markets may be less efficient because information may be limited and trading activity may be low.
Example:
A large company may be followed by 60 analysts and thousands of investors. If new information is released, the stock price may adjust within minutes.
But a small company may be followed by only 2 analysts. If new information is released, the stock price may take days or weeks to adjust.
This shows that market efficiency is not fixed. It depends on the structure, information flow, participants, and costs in the market.