Frequentist vs Bayesian Statistics in Data Science

avcontentteam 26 Dec, 2023 • 8 min read


Statistical analysis plays a crucial role in the fast-developing field of data science, enabling researchers to gain insightful knowledge from data. However, the disagreement between Bayesian and frequentist methods has always been against each other. These two strategies embody different mindsets and procedures, each offering unique benefits and drawbacks. This article compares frequentist vs Bayesian statistics, shedding light on their core ideas, primary tests employed, and key variables to consider when choosing between them.

Frequentist vs Bayesian: Overview

  Frequentist vs. Bayesian
Source: LinkedIn
AspectFrequentist ApproachBayesian Approach
Probability InterpretationObjective: Probabilities represent long-term frequencies or limiting behavior of repeated experiments.Subjective: Probabilities represent degrees of belief or uncertainty based on prior knowledge and data.
Treatment of ParametersFixed: Parameters are fixed, unknown constants. Estimation involves finding the “best” estimate based on data.Random: Parameters are treated as random variables with their own probability distributions. They are updated based on prior beliefs and data, resulting in posterior distributions.
Prior InformationN/A: Typically, prior information is not explicitly incorporated into the analysis.Crucial: Bayesian analysis involves specifying prior distributions representing prior beliefs about parameters before observing data.
Inference ApproachHypothesis Testing: Involves p-values and rejection regions.Credible Intervals: Involves credible intervals to estimate parameter values with specified probabilities.
Handling UncertaintyPoint Estimates: Point estimates (e.g., sample mean) with associated uncertainties (e.g., confidence intervals).Probability Distributions: Posterior distributions that directly model the uncertainty of parameter estimates.
Sample Size RequirementLarge Sample: Often requires a large sample size for accurate parameter estimation.Smaller Sample: Bayesian methods can provide reasonable estimates even with smaller sample sizes, especially with informative priors.
Computational ComplexitySimpler: Often involves direct formulas for parameter estimation (e.g., maximum likelihood).More Complex: Requires numerical methods like MCMC for posterior estimation, especially for complex models.
Hypothesis Testingp-values and hypothesis tests are prone to misinterpretation and controversies.Bayesian hypothesis testing uses Bayes Factors or posterior probabilities for direct comparison.
Model SelectionRelies on criteria like AIC or BIC.Model comparison using posterior model probabilities (Bayes Factors) or marginal likelihoods.
Interpretation of ResultsFocused on the data and observed effects.Results interpreted in the context of prior beliefs and their update based on data.

Let us examine their fundamental principles better to understand the disparities between frequentist vs Bayesian statistics.

What are Frequentist Statistics?

Frequentist statistics, or classical statistics, focus on making inferences about population parameters based solely on observed data. This approach assumes that probability reflects the long-term frequency of events occurring in repeated experiments. In frequentist statistics, the data is like a random sample from an underlying population, and the goal is to estimate unknown parameters or test hypotheses about them.

The Frequentist View

The frequentist statistics method concentrates on data analysis that only considers observed frequencies and sampling methods. According to this perspective, probability refers to the frequency of events occurring in repeated studies over time. 

Frequentists use p-values to determine the strength of the evidence against a null hypothesis rather than assigning probabilities to the hypotheses themselves. They strongly emphasize the significance of the observable data and leave out prior assumptions or subjective knowledge from their analysis.

What are the Main Tests Frequentists Use?

Frequentist statistics utilizes a range of tests to draw conclusions and make inferences from observed data. These tests analyze different aspects of data and assess relationships between variables. Here are some of the main tests:


Definition: T-tests determine whether the means of two groups differ statistically significantly.

Application: This test is widely used in experimental studies or A/B testing scenarios to see whether therapy or intervention has a significant impact when compared to a control group.

Chi-squared Tests

Definition: Chi-squared tests assess the independence between categorical variables in a contingency table.

Application: It is widely used to examine the relationship between two category variables, analyze survey findings, or determine whether a particular feature significantly affects the result.

Analysis of Variance (ANOVA)

Definition: ANOVA is used to compare mean differences across different groups.

Application: This test is especially useful for comparing means across three or more groups, as in experimental designs with several treatment groups or when investigating the impact of categorical variables on a continuous outcome.

Regression Analysis

Definition: Regression analysis evaluates relationships between variables, specifically between the dependent variable and one or more independent variables.

Application: This test is commonly used in a linear or logistic regression framework to analyze the impact of independent factors on a continuous outcome, forecast future values, and find relevant predictors.

Advantages and Disadvantages of Using Frequentist Statistics

Advantages of Frequentist Statistics

  • Simplicity: Frequentist methods are often easier to understand and apply, making them accessible to many users.
  • Well-established theory: Frequentist statistics have a strong theoretical foundation, well-defined properties, and extensive literature.
  • Emphasis on observed data: Frequentist statistics focus on the data and do not require prior knowledge or beliefs.

Disadvantages of Frequentist Statistics

  • Lack of flexibility: Frequentist methods can be limited when dealing with small sample sizes or complex problems requiring prior information.
  • Reliance on p-values: Using p-values for hypothesis testing has been criticized for confusing and emphasizing statistical significance rather than practical significance.
  • Failure to quantify uncertainty: Frequentist statistics frequently provide point estimates and confidence intervals but not the likelihood that a parameter falls within a certain range.

What are Bayesian Statistics?

Bayesian statistics takes a different approach, incorporating prior beliefs and updating them with observed data to obtain posterior distributions. In this framework, probability represents subjective degrees of belief rather than long-term frequencies. Bayesian statistics provides a formal mechanism to update prior knowledge and quantify uncertainty coherently.

What is Bayes’ Theorem?

Bayes’ Theorem, named for Reverend Thomas Bayes, is at the heart of Bayesian statistics. It offers a mathematical framework for revising prior ideas in the face of new data. This is the famous Bayes’ Theorem:

P(H|D) =(P(D|H) P(H))P(D)


  • P(H|D) is the posterior probability of hypothesis H, given data D
  • P(D|H) is the probability of observing data D given hypothesis H
  • P(H) is the prior probability of hypothesis H
  • P(D) is the probability of observing data D

Also Read: Naive Bayes Algorithm: A Complete guide for Data Science Enthusiasts

What are the Main Tests Bayesians Use?

Bayesian statisticians analyze data using a variety of tests and methodologies within the framework of Bayesian statistics. These methods offer a versatile and consistent approach to statistical inference. These are most common Bayesians tests:

Bayesian Hypothesis Testing

Bayesians use Bayes factors to compare the strength of evidence for different hypotheses. Bayes factors quantify the relative likelihood of the observed data under different hypotheses, allowing for the assessment of which hypothesis is more supported by the data.

Markov Chain Monte Carlo (MCMC) Methods

  • MCMC methods play a crucial role in Bayesian statistics as they allow for the sampling from complex posterior distributions. 
  • These techniques generate a sequence of samples from the posterior distribution, enabling inference and estimation of parameters of interest.

Bayesian Regression

  • Bayesian regression offers a flexible framework for modeling relationships between variables. It allows for incorporating prior information, uncertainty quantification, and estimation of posterior distributions for regression coefficients. 
  • This approach provides a more comprehensive understanding of the relationship between variables compared to traditional frequentist regression methods.

Hierarchical Models

  • Bayesian often utilizes hierarchical models to account for variability across different dataset levels. Hierarchical models capture the notion of borrowing strength from the group level to estimate parameters at the individual level. 
  • These models are particularly useful when dealing with complex data structures, such as nested or clustered data.

Bayesian Decision Theory

  • Bayesian decision theory combines statistical inference with decision-making. It incorporates the costs and benefits of different actions and uses posterior probabilities to determine optimal decisions under uncertainty. 
  • This method is useful in domains like medical diagnostics, where judgments must be made based on unclear data.

Check out: Bayesian Approach to Regression Analysis with Python

Advantages and Disadvantages of Using Bayesian Statistics

Advantages of Bayesian Statistics

  • Incorporation of prior knowledge: Bayesian statistics allows for integrating prior beliefs and expert knowledge, making it useful when dealing with limited data.
  • Coherent uncertainty quantification: Bayesian methods provide posterior distributions, allowing for the direct estimation of the probability that a parameter falls within a specific range.
  • Flexibility: Bayesian statistics can handle complex problems and small sample sizes, accommodating various modeling assumptions.

Disadvantages of Bayesian Statistics

  • Computational complexity: Bayesian approaches can be computationally demanding when working with huge datasets or complex models.
  • Subjectivity in prior specification: Choosing priors can impact the results, and subjective prior specification may introduce bias.
  • Steeper learning curve: Bayesian statistics often requires a deeper understanding of probability theory and computational methods than frequentist statistics.

Frequentist vs Bayesian: Which One Should You Choose? 

There is no one-size-fits-all solution for deciding between frequentist and Bayesian statistics. The choice is made in light of several variables, including the nature of the issue, the information at hand, any past knowledge, and the desired interpretation of the findings. Let’s examine the factors to take into account while choosing a suitable strategy:

  • Available resources: Bayesian methods often require more computational resources and specialized software than frequentist approaches.
  • Prior knowledge and beliefs: Bayesian statistics may be preferred if prior information is available or expert knowledge is crucial.
  • Interpretation of uncertainty: Bayesian statistics directly quantify uncertainty using posterior distributions, whereas frequentist statistics rely on confidence intervals.
  • Scientific community norms: Different fields have preferences and conventions regarding frequentist or Bayesian statistics.

Frequentist vs Bayesian: Can You Use Both?

Both frequentist and Bayesian methodologies can be applied in real-world data science workflows. The advantages of both paradigms can be benefited from hybrid techniques, such as Bayesian hierarchical models with frequentist hypothesis testing. 

However, careful consideration should be made on how to interpret and incorporate the findings from different approaches.

Frequentist vs Bayesian: Example

Example: Calculate the probability of getting head on a coin toss

Frequentist vs Bayesian: Example
Source: Cuemath
  • Frequentist approach: The probability of getting heads on a coin toss is calculated based on observed data. If we toss the coin 100 times and get 60 heads, the frequentist probability would be 60100=0.6
  • Bayesian approach: The probability of getting heads on a coin toss is calculated by incorporating prior beliefs and updating them with observed data. Assuming a prior probability of 0.5 (representing a fair coin), after observing 60 heads out of 100 tosses, the Bayesian would update their beliefs to calculate the posterior probability based on their chosen prior distribution and the observed data.

The likelihood would be calculated as follows:

P(B|A) = (100 choose 60) (0.5)60 (0.5)100-60

Where, (100 choose 60) is the binomial coefficient, and (0.5)60 (0.5)100-60 represents the probability of obtaining exactly 60 heads.

Plug the prior probability (0.5) and this likelihood into Bayes’ theorem, and we can calculate the posterior probability of getting heads on a coin toss.


Frequentist and Bayesian statistics offer distinct approaches to statistical analysis in data science. Frequentist methods focus on observed data and long-term frequencies, providing straightforward estimation and hypothesis testing techniques. On the other hand, Bayesian approaches consider previous assumptions and quantify uncertainty using posterior distributions. The task at hand, the data at hand, and the desired interpretation of the outcomes all impact which option is chosen between the two. While each has benefits and drawbacks, selecting the strategy that best fits the analysis’s particular requirements is crucial.

If you want to become a master of all the statistical techniques used in data science, then you can consider signing up for our Blackbelt Plus program. Explore the course curriculum here!

Frequently Asked Questions

Q1. What is the difference between Bayesian and frequentist in data science?

A. In data science, Bayesian statistics incorporate prior knowledge and quantify uncertainty using posterior distributions, while frequentist statistics solely rely on observed data and long-term frequencies.

Q2. What is the difference between Bayesian vs Frequentist statistics?

A. Bayesian statistics incorporate prior beliefs and quantifies uncertainty through posterior distributions, while frequentist statistics focuses on observed data and provides point estimates and confidence intervals.

Q3. What is the difference between frequentist and Bayesian machine learning?

A. In machine learning, frequentist methods optimize objective functions using observed data, while Bayesian methods use prior knowledge to estimate posterior distributions and quantify uncertainty.

Q4. What is the difference between Bayesian vs Frequentist statistics for dummies?

A. Frequentist statistics only use observed data to conclude population parameters, but Bayesian statistics incorporate prior beliefs and update them with observed data.

avcontentteam 26 Dec 2023

Frequently Asked Questions

Lorem ipsum dolor sit amet, consectetur adipiscing elit,

Responses From Readers

  • [tta_listen_btn class="listen"]