Investors will frequently not know why security prices fluctuate. Must look beyond security prices to underlying business value.

Security prices sometimes fluctuate, not based on any apparent changes in reality, but on changes in investor perception.

• The shares of many biotechnology companies doubled and tripled in the first months of 1991, for example despite a lack of change in company or industry fundamentals that could possibly have explained that magnitude of increase. 
• The only explanation for the price rise was that investors were suddenly willing to pay much more than before to buy the same thing.

In the short run supply and demand alone determine market prices. 

• If there are many large sellers and few buyers, prices fall, sometimes beyond reason. 
• Supply-and-demand imbalances can result from year-end tax selling, an institutional stampede out of a stock that just reported disappointing earnings, or an unpleasant rumor. 

Most day-to-day market price fluctuations result from supply- and-demand variations rather than from fundamental developments.


Investors will frequently not know why security prices fluctuate. 

• They may change because of, in the absence of, or in complete indifference to changes in underlying value. 
• In the short run investor perception may be as important as reality itself in determining security prices. 
• It is never clear which future events are anticipated by investors and thus already reflected in today's security prices. 

Because security prices can change for any number of reasons and because it is impossible to know what expectations are reflected in any given price level,  investors must look beyond security prices to underlying business value, always comparing the two as part of the investment process.


Main Point: 
Investors will frequently not know why security prices fluctuate and must look beyond security prices to underlying business value, always comparing the two as part of the investment process

Security Prices Move Up and Down for Two Basic Reasons: Business Reality or Supply and Demand

Security prices move up and down for two basic reasons:

• to reflect business reality (or investor perceptions of that reality) or 
• to reflect short-term variations in supply and demand. 

Reality can change in a number of ways,

• some company-specific, 
• others macroeconomic in nature. 

Company-specific factors

• If Coca-Cola's business expands or prospects improve and the stock price increases proportionally, the rise may simply reflect an increase in business value. 
• If Aetna's share price plunges when a hurricane causes billions of dollars in catastrophic losses, a decline in total market value approximately equal to the estimated losses may be appropriate. 
• When the shares of Fund American Companies , Inc., surge as a result of the unexpected announcement of the sale of its major subsidiary, Fireman's Fund Insurance Company, at a very high price, the price increase reflects the sudden and nearly complete realization of underlying value. 

On a macroeconomic level

These factors could each precipitate a general increase in security prices:

• a broad-based decline in interest rates, 
• a drop in corporate tax rates, or 
• a rise in the expected rate of economic growth.