strong form efficiency
Strong Form Efficiency is the idea that share prices already reflect everything, even secrets insiders know, so nobody can beat the market consistently.
In plain English
"So if my cousin at the bank tells me which stock is about to shoot up, I should buy quick quick abi?" Tunde asked, phone already halfway to his banking app.
"That is exactly what strong form efficiency says will not work," his sister Ada replied. "If the theory is true, the price of that stock has already absorbed that secret before your cousin even finished the sentence."
Strong form efficiency is the boldest version of a bigger idea called the efficient market hypothesis. It claims that share prices reflect all information that exists, public information like company results in the newspapers, and private information that only insiders such as directors, auditors or that cousin at the bank might know. If this is true, even insider trading should not give anyone an edge, because the market has somehow already priced it in.
Most people who study markets for a living think this strong version is too extreme to be fully true. That is partly why insider trading is illegal on the Nigerian Exchange and on the London Stock Exchange. If prices always absorbed insider secrets instantly and fairly, there would be no advantage to punish, yet regulators still catch people trading on tips before news breaks, which suggests prices are not quite that perfect.
Still, the idea is worth knowing because it explains why chasing hot tips from a broker, a group chat, or a relative in the diaspora who works at a big firm abroad rarely delivers the easy win people expect. Even when the tip is real, by the time you act on it, someone else may already have moved the price.
Think of it as a reminder to build wealth through patience and good research rather than through whispers, because if the market truly is this sharp, the whisper you just heard is already old news to it.
Ada tells Tunde that if a company director secretly knows profits will double next quarter, strong form efficiency claims the share price, currently ₦120, should already reflect that hidden fact. So when the news is announced and the price barely moves from ₦121, that is the theory looking almost believable, at least for that one afternoon.
Questions people ask
Is strong form efficiency actually true in real markets?
Most researchers doubt it fully holds, because insider trading still happens and sometimes still profits people before it gets caught, which a perfectly efficient market should not allow.
How is strong form different from weak form or semi strong form efficiency?
Weak form says past prices cannot help you predict future ones. Semi strong says public information like news and financial statements is already priced in. Strong form goes further, claiming even private, insider information is already reflected in the price.
Why should an everyday Nigerian investor care about this theory?
Because it is a useful check against the temptation to chase hot tips or insider gist. If markets are even somewhat efficient, steady investing and proper homework beat trying to outsmart everyone with a secret.
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