For ten points, name this hypothesis stating that a stock's price accurately and instantly reflects all known information about it.
Ivo Welch re-classified the sub-types of this hypothesis into "true believer", "firm believer", "mild believer", and "nonbeliever". Those who accept this hypothesis typically also accept a model written about by Burton Malkiel, the "random walk" model. This hypothesis is divided into strong, semi-strong, and weak forms, which differ in how they treat insider information. Most notable described by Eugene Fama, the most notable effect of this hypothesis is that it becomes impossible to arbitrage or to "beat the market". For ten points, name this hypothesis stating that a stock's price accurately and instantly reflects all known information about it.
Ivo Welch re-classified the sub-types of this hypothesis into "true believer", "firm believer", "mild believer", and "nonbeliever".
{Efficient} Market Hypothesis [accept: {EMH}]