Probability
The mathematical measure of the likelihood that a specific event will occur, expressed as a value between 0 (impossible) and 1 (certain), or equivalently as a percentage between 0% and 100%. In finance, probabilities are assigned to different investment outcomes to calculate expected returns and assess risk.
Example: A stock has a 60% probability of gaining 15% and a 40% probability of losing 10% over the next year. These probabilities help an investor calculate the expected return and decide whether the potential reward justifies the risk.
Expected Value
The probability-weighted average of all possible outcomes of an uncertain event. It is calculated by multiplying each possible outcome by its probability of occurring, then summing the results. Expected value represents the long-run average result if the same decision were repeated many times.
Example: An investment has a 70% chance of earning $1,000 and a 30% chance of losing $500. Expected value = (0.70 x $1,000) + (0.30 x -$500) = $700 - $150 = $550. On average, this investment is expected to yield $550.
Risk-Return Tradeoff
The principle that potential investment returns tend to increase as risk increases. Investors who want higher returns must accept greater uncertainty and the possibility of larger losses. This tradeoff is fundamental to portfolio theory and explains why different asset classes offer different return profiles.
Example: U.S. Treasury bonds are considered very low-risk and historically return about 2-3% per year. Stocks are riskier and have historically averaged 8-10% per year. The higher stock returns compensate investors for accepting greater volatility and the chance of significant losses.
Standard Deviation (as Risk Measure)
A statistical measure of how spread out investment returns are around their average value. A higher standard deviation means returns vary more widely from year to year, indicating greater risk. In finance, standard deviation is the most common quantitative measure of investment volatility.
Example: Fund A has an average annual return of 8% with a standard deviation of 5%, while Fund B also averages 8% but with a standard deviation of 20%. Fund B's returns swing much more wildly — from -12% to +28% in a typical range — making it significantly riskier despite the same average return.
Diversification
The strategy of spreading investments across different assets, industries, or geographic regions to reduce the impact of any single investment's poor performance on the overall portfolio. Diversification reduces unsystematic risk but cannot eliminate systematic (market-wide) risk.
Example: Instead of investing $10,000 entirely in one tech stock, an investor splits it among 20 stocks across technology, healthcare, energy, and consumer goods. If one stock drops 50%, it affects only 5% of the portfolio rather than all of it.
Systematic Risk
Risk that affects the entire market or economy and cannot be eliminated through diversification. Also called market risk or non-diversifiable risk, it includes factors like recessions, interest rate changes, inflation, and geopolitical events that impact virtually all investments simultaneously.
Example: During the 2008 financial crisis, nearly all stock prices fell regardless of individual company performance. An investor with 500 different stocks still suffered significant losses because the risk was systemic — it affected the entire market.
Unsystematic Risk
Risk that is specific to a particular company, industry, or sector and can be reduced or eliminated through diversification. Also called specific risk or diversifiable risk, it includes factors like management decisions, product failures, regulatory changes affecting one industry, or competitive pressures.
Example: A pharmaceutical company's stock drops 40% after a key drug fails clinical trials. This loss is specific to that company. An investor who held 30 different stocks across multiple industries would barely feel the impact because the loss is offset by the other holdings.
Risk Tolerance
An individual's willingness and ability to endure fluctuations in the value of their investments. Risk tolerance is influenced by factors including time horizon, financial goals, income stability, and psychological comfort with uncertainty. It determines the appropriate asset allocation for each investor.
Example: A 25-year-old saving for retirement in 40 years has a long time horizon and can afford to weather market downturns, suggesting high risk tolerance. A 60-year-old retiring in 5 years needs more stability and has lower risk tolerance, so they allocate more to bonds and less to stocks.
