What is Bayesian Statistics: Beginner’s Guide [2023]

Bayesian Statistics is a branch of Statistics that provides tools which help in understanding the probability of the occurrence of an event with respect to the new data introduced. This can also be understood as upgrading their beliefs, with the introduction of new data.

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An effective area of statistics called Bayesian statistics offers a framework for updating and fine-tuning our opinions regarding uncertain occurrences or parameters. It provides a systematic manner to take into account both old and new information to make wise judgements and forecasts. We shall examine the foundations of Bayesian decision theory, its essential ideas, and its real-world applications in this article on introduction to Bayesian statistics.

Understanding Bayesian Statistics: 

The Bayes theorem, a cornerstone of probability theory, forms the basis of Bayesian statistics. It enables us to adjust our views, or prior probabilities, in light of fresh information, producing new possibilities, or posterior probabilities. The iterative process of revising assumptions as new information becomes available forms the basis of Bayesian statistics.

Bayesian Statistics can be understood as a particular approach, for executing the concept of probability, to the basic statistical problems. This implies that it acts as a mathematical tool which helps in strengthening our belief about certain events with respect to new data or new evidence concerning these events. This can simply be understood as the prediction of the outcome of events, when two events are supplementary to each other.

Hence, the inference (Bayesian) interprets the probability, which is a measure of conviction of, say, confidence that a particular person may possess with regard to the occurrence of the particular event.

A preconceived notion about the belief may exist about the event, but it again becomes subject to change as soon as new data is introduced. And it is very logical to assume so. Hence, Bayesian statistics comes extremely handy in such situations when these events are to be analyzed, along with the new evidence introduced. It is a mathematical tool that helps in the up-gradation of our belief regarding the event and the new data, which is so introduced.

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Key Bayesian Statistics Concepts

  • Prior probability: Prior probability is our initial assessment of the likelihood of an event occurring before we have any supporting data
  • Probability: The probability measures how strongly the data support various potential values for the parameters in a statistical model
  • Posterior Probability: The revised belief following consideration of the prior probability and the likelihood is known as the posterior probability
  • The process of employing Bayes’ theorem to determine the posterior probability distribution and make predictions or inferences based on the data is known as Bayesian inference
  • Prior Sensitivity: Prior sensitivity refers to the influence of several prior hypotheses on the posterior probability distribution
  • Markov Chain Monte Carlo (MCMC): To approximate complicated posterior distributions, MCMC techniques are frequently used in Bayesian statistics

Comparison of Classical Statistics and the Bayesian Statistics

Usually, when Bayesian Statistics is spoken about, a contrasting statistical inference is also always mentioned, which is the classical or the frequentist statistics and belongs to the school of thought that believes that the probabilities are merely the frequency of the events that occur in the long run, of the repeated trials. Hence when the statistical inferences are carried out, there are two approaches for the same, being the Frequentist, and Bayesian, which are therefore two very different philosophies.

What Frequentist Statistics does is that it eliminates the uncertainty by giving estimates. On the other hand, Bayesian Statistics makes an effort to accommodate the uncertainty and define it and make adjustments to the beliefs of the individuals.

Hence, a Bayesian Interpretation mainly consists of probability, which is the ‘summary of an individual’s opinion. It is also important to note that different individuals have different opinions since they have different mechanisms of interpreting the data.

In this particular framework, a person has to choose the probability of 0 when they don’t have confidence in the occurrence of the event, while 1 will be picked when the person is positive about the occurrence of the event. If the probability so given is between 0 and 1, then this opens doors for several outcomes.

To better understand Bayesian Inference, it is extremely important to carry out and understand the Bayes Rule, and then interpret it in the correct manner. The application of conditional probability can hence derive the Bayes Theorem.

Bayesian statistics applications

  • Making decisions: A formal framework for making decisions in the face of uncertainty is provided by Bayesian statistics. Decision-makers can use it to quantify the expected value of several options and select the best course of action.
  • Predictive Modelling: By incorporating prior knowledge and updating them as new data becomes available, Bayesian statistics enables the building of reliable predictive models. It is extensively utilised in industries including banking, medicine, and marketing.
  • Bayesian statistics provides a versatile method for estimating unknown parameters in statistical models while taking uncertainty into account and using prior knowledge.
  • By choosing sample sizes and resource allocations that maximise the information gained, Bayesian approaches help to optimise the design of experiments.
  • Machine learning: Bayesian inference gives machine learning algorithms a probabilistic framework that enables the measurement of uncertainty and enhances model performance.

Read: Bayesian Networks

Help in Understanding and Interpreting Bayes Rule for Executing the Bayesian Inference

As stated before, the main idea of the Bayesian Inference is to upgrade any of our beliefs about the events as any new data is presented with. This is a more organic way to talk about the probable events. As more data is accumulated, the previous beliefs get washed out.

One example through which this can be explained is to consider the Moon’s prior belief is to collide with Earth. With the passage of every night, if we were to consider these events with regard to the Bayesian Inference, it will tend to modify some of our previous beliefs, that it is very less likely that the Moon will be colliding with the Earth. The belief that the Moon is likely to remain in its orbit is going to be reinforced.

Also, to follow up the concrete probability, a coin flip example of the Bayesian inference.

It is very significant to understand that the concept can be mathematically applied. A significant aspect of understanding the Bayesian Inference is the understanding of the parameters and models.

Models are the main mathematically formulated events. The parameters, therefore, are the factors of the models that affect the data. In the example of observing the fairness of the coin, it is defined as the parameter denoted by (theta). The outcome, let’s assume as A. The question that we can answer with the data at hand:

The outcome, which is given as (A), determines the probability of the coin being fair. (theta=0.5)

When we use the data to numerically represent it using the Bayes Theorem, the formula which presents itself:

P(Ф/A) = [P(A/Ф)*P(Ф)/P(A)]

P(Ф) here refers to the prior strength of our belief, which was with regard to the fairness of the coin before the toss. Here the probability of the fairness of the coin levitates between 0 and 1.

P(A/Ф) = This signifies the probability of observing the result of our distribution of theta. In simpler terms, if the coin was fair, the probability of observing the number of heads in the particular number of flips is observed.

Must Read: Naive Bayes Explained

P (Ф/D hence observes the past belief of our parameters, after taking new data into consideration, which is new heads.

For an effective definition of the models, it is important to understand that the models themselves need to be defined effectively, that too beforehand. Firstly, it shows the likelihood function, which is represented by P(D/Ф), while others show prior beliefs. The product then gives the past belief function, which is P(Ф/A).

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Bayesian statistics gives us a potent toolbox for reasoning under uncertainty, enabling us to combine our prior assumptions with fresh data to arrive at well-informed decisions and predictions. It provides a versatile and understandable method for parameter estimation, predictive modelling, and statistical inference. We can improve our comprehension of complicated systems and make more reliable decisions by adopting Bayesian concepts. Bayesian statistics are still a useful technique for deriving important insights from data in a variety of disciplines, even as the science of data analysis develops further.


Hence, Bayesian Statistics then exists as a framework for describing the perfect case of uncertainty, with the help of mathematics and the tool of probability. On a very simple level, the ‘classical’ outlook for performing the inference very closely looks like the Bayesian Statistical Method, which involves making a prior assumption.

In a nutshell, the frequentists take the relative chance of datasets, as compared to the Bayesian Inference. The information which is so provided here has been explained in a very basic and simple manner, which is enough for any individual to gather the fundamentals of the core concept.

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What is a limitation of Bayesian statistics?

Bayesian statistics is a set of techniques for analyzing data that arise from a set of random variables. It works on the probability distribution of the parameters and can be used to make inference about parameters. It has some limitations, like the probabilistic approach is not valid for many scientific applications. Bayesian statistics is a very powerful tool in statistics that allows coming up with the best possible solution to a problem. However, it only works when there is enough data. In a case where there isn’t enough data, the Bayesian solution does not work.

What are the applications of Bayesian statistics?

Bayesian statistics is applied to fields such as medicine and engineering. In medicine, Bayesian statistics are used for medical diagnosis, especially for hard medical conditions. For example, Bayesian statistics can be used to estimate the probability of a cancer to spread to other organs based on some imaging data. Another field where Bayesian statistics are widely used is bioinformatics. Bayesian statistics are used to identify DNA sequence alignments in biological databases. Another field that relies on Bayesian statistics is engineering. In the field of engineering, Bayesian statistics are utilized in reliability analysis, software testing, and many other engineering analyses.

What is the major advantage of Bayesian inference?

One major advantage of Bayesian inference is that, unlike other forms of inference, the role of data is explicitly represented. While the results of an experiment can never prove a theory correct and can also never prove it incorrect, Bayesian inference can nevertheless make statements about the probability that a given theory is correct. This is an advantage over many other forms of inference in which the data is either ignored or given no role.

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