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Expected Value: Definition, Formula & Examples

Written by Paul Boyce Posted in Econometrics
Last Updated July 21, 2023

What is Expected Value?

In the realm of statistics and probability theory, expected value plays an integral role, providing a simple yet powerful mechanism for assessing possible outcomes of different scenarios. The expected value of a random variable essentially provides us with a central or ‘expected’ outcome when the random variable undergoes a particular experiment multiple times.

At its core, the expected value is a weighted average of all possible values that a random variable can take on, with each value being weighted according to its probability of occurrence. It forms the backbone of numerous disciplines, including but not limited to finance, economics, game theory, and insurance, among others. It helps decision-makers understand the potential outcomes and risks involved in different scenarios and make informed decisions.

Key Points

The expected value formula calculates the average outcome of a probability distribution.
It is obtained by multiplying each possible outcome by its corresponding probability and summing them.
The expected value is used to estimate the average return or outcome of a random variable or uncertain event.

Understanding Expected Value

Expected value, often denoted as E(X), is a fundamental concept in probability theory and statistics. It represents the average or mean value considering each outcome’s probability in a series of events or experiments.

The expected value is calculated as the weighted average of all possible values of a random variable, where each value is weighted by the probability of its occurrence. It provides a measure of the center of the distribution of the variable.

The concept of expected value has both theoretical and practical applications. It is used in various fields, such as investment analysis, gaming, insurance, and decision-making under uncertainty.

It is important to understand that the expected value represents the average outcome over a large number of trials or experiments. It does not guarantee that this outcome will occur in a single experiment.

The concept of expected value relies on the Law of Large Numbers, which states that as the number of trials of a random event increases, the experimental probability of the event tends to its theoretical probability.

Expected Value Formula

The formula for calculating the expected value (EV) of a discrete random variable is given as:

EV = Σ [xi * P(xi)]

where:

xi represents each value in the dataset
P(xi) is the probability of each of these values occurring

To compute the expected value, each possible value of the random variable is multiplied by its probability of occurring. The results are then summed to obtain the expected value.

In the case of a continuous random variable, the expected value is given by the integral of the product of the variable and its probability density function.

The formula can be expanded for scenarios with multiple possibilities. For example, in a game of chance like a lottery, the formula would include every possible outcome and its respective chance of occurring.

It’s important to note that the formula assumes accurate knowledge of probabilities and truly random outcomes. If these assumptions don’t hold, the expected value may not accurately predict the average outcome over many trials.

The formula provides a central location measure for a probability distribution, with the expected value being the center of mass of the distribution. It is useful in comparing different random variables, determining optimal strategies in game theory, economics, and risk-neutral valuation in finance.

How to Calculate Expected Value

The expected value of a random variable gives us a long-run average value of the variable over many independent repetitions of the experiment. It is typically calculated using the following steps:

Identify Possible Outcomes List all possible outcomes that can be achieved from a certain event or situation.
Determine the Probability of Each Outcome Determine the probability of each outcome, either from historical data, a mathematical model, or a fair assumption.
class=”styled”>Multiply Each Outcome by its Probability Multiply each outcome by its respective probability to obtain the ‘weighted’ value of each outcome.
Sum Up All the Values Sum up all the weighted values. This sum is the expected value.

Let’s use a dice roll as an example:

The possible outcomes are 1, 2, 3, 4, 5, and 6.
Since a fair die has six faces, each with one unique number, the probability of any number showing up is 1/6.
Multiplying each outcome by its probability: 1*(1/6), 2*(1/6), 3*(1/6), 4*(1/6), 5*(1/6), 6*(1/6).
Summing up the values: (1/6) + (2/6) + (3/6) + (4/6) + (5/6) + (6/6) = 3.5.

This means that if we were to roll a die many times, we would expect the average value of the results to be about 3.5.

Remember, when calculating the expected value, each probability must be between 0 and 1, and the sum of all probabilities must equal 1.

Interpreting Expected Value

The expected value is a key concept in probability, statistics, and related fields. When you interpret the expected value, you’re essentially looking at the long-term average or mean of a random variable over the course of many repeated experiments or trials.

Long-Term Average The expected value does not predict the outcome of a single event but rather describes the average outcome over many events.
Measure of Central Tendency The expected value is a measure of the center of the probability distribution of a random variable. It provides a single summary number that reflects the center of the probability distribution, much like the mean in descriptive statistics.
Weighted Average Expected value can be considered as a weighted average of all possible values of a random variable, where each value is weighted by its probability of occurrence. It is therefore not simply the arithmetic mean of values.
Prediction In a predictive or forecasting context, the expected value can provide an estimate of what to expect for a future data point or over many data points, assuming the probability distribution is known or accurately estimated.

Remember, interpretation of expected value depends on context. In some scenarios, an expected value may be exactly what is needed. In other scenarios, different measures may be more applicable.

Applications of Expected Value

The concept of expected value is widely used in various fields such as economics, finance, statistics, and game theory. Here are some of its primary applications:

Economics and Finance Expected value plays a crucial role in financial decision-making, where uncertain outcomes are the norm. Investors use expected value to determine the expected return on an investment, considering all possible outcomes and their probabilities.
Insurance In the insurance industry, expected value is used to price policies. Insurers calculate the expected value of potential losses from specific risks to determine the premiums.
Game Theory Expected value is used to predict the outcome of games or decisions involving uncertainty, helping players devise optimal strategies.
Statistics and Data Analysis Expected value is a fundamental concept in statistics, used in probability problems and complex statistical inference procedures.
Quality Control and Risk Assessment Expected value is used in quality control to assess the average performance of a product or process, and in risk assessment to quantify the potential impact of a risk.
Public Policy Expected value is used in cost-benefit analysis to evaluate the expected outcomes of different policy options.

Remember, despite its wide-ranging applications, expected value is just one of many tools available for making decisions under uncertainty. Depending on the situation, other methods such as scenario analysis, decision trees, or Monte Carlo simulations may be more appropriate.

Limitations of Expected Value

While the expected value is a useful measure in probability and statistics, it’s essential to recognize its limitations:

Assumes Known Probabilities Expected value calculations assume exact knowledge of probabilities, which may not be available in real-world situations.
Sensitive to Outliers Extreme values or outliers can significantly impact the expected value, even if they have low probabilities of occurring.
Doesn’t Account for Risk Preferences Expected value does not consider individuals’ risk attitudes or their aversion to uncertain outcomes.
Lacks Context Expected value does not provide information about the variability or distribution of outcomes, which can be crucial for decision-making.
Simplification of Complexities Expected value calculations may oversimplify complex decisions that involve multiple variables and uncertainties.

These limitations don’t negate the usefulness of expected value, but they highlight the need for careful consideration and appropriate application, considering its assumptions and potential shortcomings.

Examples of Expected Value

Example 1: Simple Dice Game

Consider a simple dice game where you roll a six-sided die and win a prize based on the number rolled. The cost to play the game is $3.50. Let’s calculate the expected value:

Expected Value = (1/6 * $1) + (1/6 * $2) + (1/6 * $3) + (1/6 * $4) + (1/6 * $5) + (1/6 * $6) – $3.50 = $0.50

The expected value is positive, indicating that, on average, you would expect to win 50 cents per game in the long run.

Example 2: Lottery Ticket

Suppose you buy a lottery ticket for $2. The probability of winning the jackpot is 1 in 200,000, and the jackpot is $100,000. Let’s calculate the expected value:

Expected Value = (1/200,000 * $100,000) – $2 = -$1.50

Even though the possible prize is large, the expected value is negative because the probability of winning is very low compared to the cost of the ticket. In the long run, you would expect to lose $1.50 for every ticket you buy.

These examples demonstrate how expected value can be used to assess the potential costs and benefits of different choices. However, it’s important to consider the limitations and context of each situation.

FAQs

What is the expected value formula?

The expected value formula calculates the average outcome of a probability distribution by multiplying each possible outcome by its corresponding probability and summing them.

How is the expected value formula used?

The expected value formula is used to estimate the average outcome or expected return of a random variable or uncertain event.

What is the significance of the expected value?

The expected value provides a measure of central tendency and helps in decision-making by providing insight into the potential outcomes and their probabilities.

Can the expected value be negative?

Yes, the expected value can be negative if there are outcomes with negative values and their corresponding probabilities are taken into account.

About Paul

Paul Boyce is an economics editor with over 10 years experience in the industry. Currently working as a consultant within the financial services sector, Paul is the CEO and chief editor of BoyceWire. He has written publications for FEE, the Mises Institute, and many others.