Complete Guide to Types of Probability Distributions: Examples Explained
Updated on Jun 26, 2025 | 8 min read | 19.97K+ views
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Updated on Jun 26, 2025 | 8 min read | 19.97K+ views
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Do you know? A recent Nature article applied extended Rayleigh-type distributions to medical data, particularly in the context of COVID-19 modeling. Weibull distributions, crucial in reliability engineering, are widely used in 2025 for modeling wind speed, component failure, and hydrology. |
Probability distributions describe how a random variable’s values are spread across possible outcomes. They are essential in statistics for modeling uncertainty, analyzing patterns, and making data-driven decisions. These distributions help estimate the likelihood of outcomes in scientific, engineering, financial, and machine learning tasks.
There are two main types: discrete distributions (such as binomial and Poisson) for count-based outcomes, and continuous distributions (like usual and exponential) for measurable quantities. Each type has distinct mathematical formulas and real-world use cases. This guide explains these types of probability distributions with clear definitions, formulas, graphs, and practical examples to strengthen your understanding.
To understand types of probability distributions, you must first understand statistics and probability as the core building blocks.
Statistics: It is the science of collecting, analyzing, interpreting, and presenting data. It helps you make sense of raw numbers using mathematical techniques. In data science, statistics is essential for identifying patterns, drawing conclusions, and converting large volumes of data into actionable insights.
Probability: It measures the likelihood that a specific event will occur. The value ranges from 0 to 1, where 0 indicates that the event is impossible, and 1 indicates that it is certain to occur. For example, if there is a 60 percent chance of rain tomorrow, the probability is 0.6. Probability is used daily, from risk estimation in business to modeling events in medicine and engineering. It allows you to make predictions based on observed or expected patterns.
Ready to put your knowledge of probability and statistics into practice? Learn how these concepts power real-world AI systems across healthcare, finance, and automation. Explore our top AI courses below, designed to help you build strong foundations:
Probability Distributions: This describes how probabilities are assigned to each possible outcome in a random experiment. These distributions can be expressed using tables, formulas, or graphs. A simple example is the result of tossing two coins. The distribution of outcomes can be shown as:
Number of Heads | Probability |
0 | 0.25 |
1 | 0.50 |
2 | 0.25 |
Types of probability distributions apply to both simple and complex situations. They are used to model random events such as vaccine response rates, customer arrivals, or component failures.
Also Read: What is Probability Density Function? A Complete Guide to Its Formula, Properties and Applications
Probability distributions are key in statistical modeling, helping us understand data behavior and predict outcomes. They describe how probabilities spread across random variable values, either discrete (countable) or continuous (within a range). Choosing the right distribution allows for accurate predictions and effective modeling in areas like quality control and forecasting.
Discrete distributions handle countable data, while continuous ones model variables like time or temperature. Understanding their features is essential for selecting the appropriate model for your analysis. Let’s explore each of these below in depth!
A discrete probability distribution describes the probability of occurrence for each value of a discrete random variable, which takes countable values. Examples include non-negative integers or other finite, countable quantities. Discrete variables cannot assume all possible values in a given range; they only take specific, isolated values.
Key Features:
Example: The probability of rolling a 3 on a six-sided die can be expressed as P(X = 3) = 1/6.
where x represents possible outcomes, and P(X=x) is the associated probability of each outcome. The expected value provides the long-term average or center of the distribution.
Example: For a fair six-sided die, the expected value would be E[X]=(1/6)×(1+2+3+4+5+6)=3.5.
where μ is the mean of the distribution. A higher variance indicates a larger spread of outcomes.
Example: For a binomial distribution, variance is calculated based on the number of trials and the probability of success.
Common Distributions:
Example: A coin toss has a 50% chance of landing heads (success) and a 50% chance of landing tails (failure).
Example: Tossing a coin 10 times and counting the number of heads follows a binomial distribution.
Example: Modeling the number of emails received in an hour or the number of customer arrivals in a store.
Example: The number of rolls of a die until you roll a 6.
Applications:
A continuous probability distribution describes the probability of occurrence of each value for a continuous random variable, which can take any value within a given range. These variables often represent measurements and can take an infinite number of values within the range, such as height, time, or temperature.
where f(x) is the PDF.
Example: For a normal distribution, the probability of a value falling within a certain range is determined by the area under the bell curve between those two points.
where x represents possible outcomes and f(x) is the PDF of the distribution. The expected value indicates the "center" or average value of the distribution.
where μ s the mean. The variance indicates how spread out the values are around the mean.
Common Distributions:
Example: Heights of people or test scores tend to follow a normal distribution.
Example: The roll of a fair die or random number generation within a specific range.
Example: The time between arrivals of buses at a stop.
Example: Modeling the probability of success in a project with a known success rate.
Applications:
Below is a comparative overview of the key features, formulas, and common applications of discrete and continuous probability distributions to help you understand their differences and uses.
Feature |
Discrete Distributions |
Continuous Distributions |
Definition | Deals with countable values (e.g., integers). | Models variables that can take any value within a range. |
Probability Calculation | Uses Probability Mass Function (PMF) | Uses Probability Density Function (PDF) |
Example Applications | Modeling counts (e.g., number of successes, defective items) | Modeling measurements (e.g., height, temperature, time) |
Probability Representation | Defined at specific points (e.g., P(X = x)) | Represented as an area under the curve (e.g., P(a ≤ X ≤ b)) |
Real-World Usage | Quality control, game outcomes, survey results | Financial modeling, time analysis, environmental data |
Calculation Methods | Summing over all possible outcomes | Integrating over the continuous range of outcomes |
Now that you have covered the fundamentals of discrete probability distributions, let's explore some of the most common types and their specific applications.
Understanding the various discrete probability distributions is crucial for accurately modeling different types of data and phenomena. Each distribution has its own unique characteristics and applications. Below is an brief explanation of the most commonly used discrete distributions:
The Bernoulli distribution models the outcome of a single binary trial with two possible results: success (1) or failure (0). This is one of the simplest discrete distributions, often used to model situations like coin flips or yes/no questions.
Bar chart representing the Bernoulli distribution. It shows the two possible outcomes (0 and 1), with their corresponding probabilities: 1−p1 - p1−p for failure (0) and ppp for success (1).
Key Features:
where p is the probability of success.
Applications: Modeling binary outcomes like pass/fail tests, win/loss games, or success/failure events.
Also Read: Binomial Distribution in Python: Implementation, Examples & Use Cases
The binomial distribution models the number of successes in a fixed number of independent Bernoulli trials. Each trial has the same probability of success. It’s widely used for problems involving a series of repeated, independent trials with two possible outcomes.
Here is the histogram representing the binomial distribution for the number of successes across multiple trials. As the number of trials nnn increases, the distribution tends to form a bell-shaped curve, showing the probability of different outcomes based on the given probability of success p.
Key Features:
where C(n,x) is the binomial coefficient.
Applications: Estimating the number of successes in scenarios like quality control (e.g., number of defective items in a batch) or election predictions (e.g., number of votes for a candidate).
Also Read: Beyond Data: The Power of Subjective Probability!
The Poisson distribution models the number of events that occur within a fixed interval of time or space. It assumes that events happen independently and at a constant average rate, often applied in situations where events are rare or infrequent.
Right-skewed curve representing the Poisson distribution. It shows the probability of a given number of events occurring, with a peak near the mean (λ), and the distribution typically becomes more skewed to the right as the rate of occurrence increases.
Key Features:
where λ is the average rate of occurrence.
Applications: Modeling rare events, such as the number of phone calls received by a call center or the number of accidents at a busy intersection.
Also Read: Top Probability Aptitude Questions & Answers [2025]
The geometric distribution models the number of trials required to achieve the first success in a sequence of independent Bernoulli trials. Each trial has a constant probability of success, making this distribution suitable for problems involving the number of attempts before the first success.
The decreasing exponential curve representing the geometric distribution. It shows the probability of achieving the first success, with the probability decreasing as the number of trials increases. The distribution is skewed to the right, reflecting the higher likelihood of success occurring earlier in the trials.
Key Features:
where p is the probability of success.
Applications: Modeling situations such as the number of coin flips until the first heads or the number of sales calls until a successful sale.
The negative binomial distribution generalizes the geometric distribution by modeling the number of trials needed to achieve a specified number of successes, rather than just one.
The distribution curve representing the Negative Binomial distribution. It shows the probability of achieving the r-th success after a certain number of trials, with the distribution typically skewed to the right as the number of trials increases to reach the desired number of successes.
Key Features:
where r is the number of successes required.
Applications: Modeling scenarios where a fixed number of successes is required, such as the number of sales calls needed to close a certain number of deals.
Also Read: Basic Fundamentals of Statistics for Data Science
The hypergeometric distribution models the number of successes in a fixed number of draws from a finite population, without replacement. Unlike the binomial distribution, the probability of success changes with each draw.
Bar chart representing the Hypergeometric distribution. It illustrates the probability of success in a fixed number of draws from a finite population without replacement. The distribution typically shows more skewness compared to the binomial distribution, especially when the sample size is large relative to the population size.
Key Features:
where N is the total population size, K is the number of successes in the population, and nnn is the number of draws.
Applications: Used in quality control and survey sampling where the sample is drawn without replacement, such as determining the number of defective items in a batch or evaluating survey responses.
Now that you have explored the key discrete distributions, let's explore the common continuous probability distributions and understand how they model data that can take any value within a range.
Continuous probability distributions are fundamental in statistical modeling, especially when dealing with data that can take any value within a range. Unlike discrete distributions, which handle countable outcomes, continuous distributions describe variables that can assume an infinite number of values. Understanding these distributions is crucial for tasks such as data analysis, hypothesis testing, and predictive modeling.
Below, you will explore some of the most commonly used continuous probability distributions:
The uniform distribution is a continuous probability distribution where all outcomes are equally likely within a specified range [a,b]. It is often referred to as the rectangular distribution due to its constant probability density function (PDF).
Key Features:
where a and b are the minimum and maximum values, respectively.
Applications: Modeling scenarios where all outcomes within a range are equally likely, such as random number generation or simulating fair dice rolls.
Also Read: Statistical Programming in Machine Learning: Contrast Between Pyro and TFP
The normal distribution, also known as the Gaussian distribution, is a continuous probability distribution characterized by its bell-shaped curve, symmetric around the mean. It is widely used in statistics due to the Central Limit Theorem, which states that the sum of a large number of independent, identically distributed variables will be approximately normally distributed.
Key Features:
where μ is the mean and σ2 is the variance.
Applications: Modeling natural phenomena such as heights, weights, and test scores, where data tends to cluster around a central value.
Also Read: Power Analysis in Statistics: Definition & Execution Guide
The exponential distribution is a continuous probability distribution that models the time between events in a Poisson process, where events occur continuously and independently at a constant average rate.
Key Features:
where λ is the rate parameter.
Applications: Modeling waiting times between events, such as the time between arrivals of customers at a service center.
The gamma distribution is a two-parameter family of continuous probability distributions that generalizes the exponential distribution. It is used to model the time until an event occurs k times, where k is a positive integer.
Key Features:
where k is the shape parameter, θ is the scale parameter, and Γ(k) is the gamma function.
Applications: Modeling waiting times for multiple events to occur, such as the time until a machine breaks down after several uses.
Also Read: Gaussian Naive Bayes: Understanding the Algorithm and Its Classifier Applications
The beta distribution is a family of continuous probability distributions defined on the interval [0,1], parameterized by two positive shape parameters, α and β.
Key Features:
where B(α,β) is the beta function.
Applications: Modeling random variables that are constrained to intervals of finite length, such as proportions or percentages.
A log-normal distribution is a continuous probability distribution of a random variable whose logarithm is normally distributed. It is used to model variables that are positively skewed.
Key Features:
where μ is the mean and σ2 is the variance of the natural logarithm of xxx.
Applications: Modeling stock prices, income distributions, and other variables that cannot be negative and are positively skewed.
The chi-square distribution is a special case of the gamma distribution with k/2k/2k/2 degrees of freedom. It is widely used in statistical inference.
Key Features:
Applications: Used in hypothesis testing, particularly in the chi-square test for independence and goodness of fit.
The Student’s t-distribution is a continuous probability distribution that arises when estimating the mean of a normally distributed population in situations where the sample size is small and the population standard deviation is unknown.
Key Features:
where ν is the degrees of freedom.
Applications: Used in hypothesis testing and constructing confidence intervals, especially when dealing with small sample sizes.
Selecting the appropriate probability distribution is crucial for accurate statistical analysis and modeling. The choice depends on various factors, including the nature of the data, sample size, distribution shape, and statistical moments.
Here's a structured approach to guide your selection process:
When dealing with count data (e.g., number of occurrences), consider distributions like:
For modeling time until an event occurs, consider:
When dealing with data that represent ratios or proportions, such as success rates, the Beta Distribution is appropriate. It models variables constrained to the interval [0, 1], making it ideal for proportions.
For small sample sizes (typically n < 30), the choice of distribution should be based on the underlying population distribution. If the population is normal, the sample mean will also be normally distributed.
According to the Central Limit Theorem, for large sample sizes (n ≥ 30), the sampling distribution of the sample mean will approximate a normal distribution, regardless of the population's distribution.
Examine the histogram or density plot of your data:
Visual inspection of data distributions can provide initial insights into the appropriate distribution.
Quantifies the asymmetry of the distribution.
Measures the "tailedness" of the distribution.
A statistical test that assesses whether sample data have the skewness and kurtosis matching a normal distribution. A significant result suggests the data do not follow a normal distribution.
Having understood how to select the appropriate probability distribution, let's now explore the key parameters that define each type and their role in shaping data modeling
Understanding the key parameters of probability distributions is essential for selecting the appropriate model and interpreting the results. These parameters help describe the characteristics of the distribution and play a crucial role in determining the behavior of the data.
Below are the most important parameters that define the types of probability distributions:
where xi represents the possible values and P(X=xi) their respective probabilities. For continuous distributions, the mean is calculated using the integral of the distribution’s probability density function (PDF).
The mean helps us understand where most of the data is centered.
2. Skewness and Kurtosis
Where N is the sample size, xi are the values, μ\muμ is the mean, and σ\sigmaσ is the standard deviation.
Positive Skew: Data with a long right tail. Examples include income distributions and age at retirement.
Negative Skew: Data with a long left tail. Examples include exam scores, where most students perform well but a few perform poorly.
A kurtosis greater than 3 indicates leptokurtic (heavy-tailed) distributions, while a kurtosis less than 3 indicates platykurtic (light-tailed) distributions.
3. Probability Mass vs. Probability Density Functions
The sum of probabilities across all possible outcomes must equal 1.
Example: In a coin toss, the PMF would define the probability of getting heads or tails.
Probability Density Function (PDF): The PDF applies to continuous probability distributions and defines the probability of the random variable falling within a particular range of values. Unlike the PMF, the probability of any single value is technically 0 for a continuous variable. Instead, probabilities are calculated as the area under the curve over a range of values:
The PDF must satisfy:
Example: In a normal distribution, the PDF would define the probability density of the variable falling between two values.
By understanding these key parameters, you can better analyze and select the appropriate probability distribution for your data, ensuring accurate modeling and insightful analysis.
Also Read: Math for Data Science: Linear Algebra, Statistics, and More
Having covered the key parameters of probability distributions, let's now explore some practical examples to see how these distributions are used in real-world scenarios.
Understanding the practical applications of probability distributions can greatly enhance your ability to model and analyze real-world data. Here are some common scenarios where different types of probability distributions are applied:
The Bernoulli distribution is used to model the outcome of a single binary trial, like tossing a fair coin. It has only two possible outcomes: success (1) or failure (0), with each trial having a probability of success p and a probability of failure 1−p, in the case of a fair coin, p=0.5.
Example: Tossing a coin once, where the outcome is either heads (success) or tails (failure), follows a Bernoulli distribution.
The binomial distribution is an extension of the Bernoulli distribution and models the number of successes in a fixed number of independent Bernoulli trials. If you toss a fair coin multiple times (e.g., 10 times), the number of heads that appear follows a binomial distribution.
Example: If you toss a coin 10 times, the binomial distribution can be used to calculate the probability of getting exactly 3 heads.
The exponential distribution is often used to model the time between events in a Poisson process, such as the time between customer arrivals at a call center. It assumes that the events occur continuously and independently at a constant average rate λ.
Example: If the average time between customer calls at a call center is 5 minutes, the exponential distribution can model the waiting time between two successive calls.
The normal distribution, also known as the Gaussian distribution, is commonly used to model continuous data that tends to cluster around a mean value.
Example: The heights of adult women in a population may follow a normal distribution with a mean of 64 inches and a standard deviation of 3 inches. Most women’s heights would fall near this mean, with fewer women being much taller or shorter.
The Poisson distribution is used to model the number of events occurring within a fixed interval of time or space, particularly when these events occur at a constant rate and are independent of each other.
Example: If a website receives an average of 5 visitors per minute, the Poisson distribution can be used to model the probability of having 3 visitors in the next minute or 7 visitors in the next minute.
These examples demonstrate how probability distributions are applied in diverse fields, ranging from simple binary outcomes to modeling time intervals and continuous data. Understanding these applications will enable accurate data analysis and informed decision-making based on probability models.
When solving problems involving probability distributions, it’s essential to approach the task methodically to select the appropriate distribution and use the right techniques. Understanding the data's characteristics and the problem's context is crucial for making the correct choice.
Here are some tips to guide the process:
By following these tips, you can systematically analyze problems involving probability distributions, ensuring you select the right distribution and apply the appropriate methods to find solutions.
Understanding probability distributions is key to applying data science effectively. It involves knowing their types, use cases, and formulas, and gaining hands-on experience with real examples. These distributions help model uncertainty, test hypotheses, and draw predictive insights from data.
Many learners struggle to apply theory in practical scenarios. Practicing with datasets and choosing the right distribution sharpens understanding. upGrad supports this journey with expert mentorship, structured programs, and real-world projects that turn concepts into job-ready skills. Below are some extra courses that will help you ace artificial intelligence and data science:
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References:
https://www.nature.com/articles/s41598-025-03645-w
https://en.wikipedia.org/wiki/Weibull_distribution
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