Investor's wiki

Base Rate Fallacy

Base Rate Fallacy

What Is Base Rate Fallacy?

Base rate fallacy, or base rate neglect, is a cognitive mistake by which too little weight is put on the base, or original rate, of possibility (e.g., the probability of A given B). In behavioral finance, base rate fallacy is the propensity for individuals to judge the probability of a situation by not considering all important data wrongly. All things being equal, investors could zero in additional vigorously on new data without recognizing how this effects original suspicions.

Grasping Base Rate Fallacy

While considering base rate data, two categories exist while determining probability in certain situations. The first is general probability, while the second is event-explicit data, for example, the number of basis points the market has moved, which percentage a company is off in its corporate earnings, or how frequently a company has changed management. Investors frequently will generally give more weight to this event-explicit data over the setting of the situation, now and again disregarding base rates altogether.

While frequently event-explicit data is important in the short-term, particularly for traders or short-venders, it can increasingly pose a threat than it necessities to for investors endeavoring to anticipate the long-term direction of a stock. For instance, an investor might be attempting to determine the probability that a company will outperform its peer group and arise as an industry leader.

Many examples exist in which feeling and psychology vigorously influence investor choices, making individuals act in erratic ways.

While the base of information⁠ — the company's strong financial position, steady growth rates, management with proven histories, and an industry with strong demand⁠ — all point to its ability to outperform, a weak earnings quarter could set investors back, making them think that this is shifting the company's direction. As is all the more frequently the case, it could basically be a small blip in its overall rise.

Special Consideration: Behavioral Finance

Behavioral finance is a moderately new field that tries to join behavioral and cognitive mental theory with conventional economics and finance to give clarifications to why individuals settle on irrational financial choices. As indicated by conventional financial theory, the world and its participants are, generally, consistent "abundance maximizers."

With strong connections to the concept of base rate fallacy, overreaction to a market event is one such model. As per market proficiency, new data ought to quickly be reflected in a flash in a security's price. Reality, nonetheless, will in general go against this theory. Frequently, market participants go overboard to new data, for example, a change in interest rates, making a bigger than-fitting effect on the price of a security or asset class. Such price floods are not typically permanent and will more often than not disintegrate after some time.


  • This trader "blunder" is concentrated vigorously, as oftentimes emotional inclinations, for example, base rate fallacy drive market course.
  • Base rate fallacy is the point at which the base or original weight or probability is either disregarded or thought about secondary.
  • Behavioral finance includes the study of base rate fallacy and its market effects.