Coursera Learner working on a presentation with Coursera logo and
Coursera Learner working on a presentation with Coursera logo and

Bias and Variance are two main prediction errors that mostly occur during a machine learning model. Machine learning solves numerous problems that we worry about. Through machine learning, we can perform activities that we were not able to perform before.

As machine learning solves most of the problems, we face various challenges. These predictions can be threatening and will affect the outcome of the mode. That is why we need to understand and solve these predictions.

To design a machine learning model, we need to feed all the important data so the model can make predictions and develop new data on its own. Variances will make a fit model different from the parameters you set. Dealing with variances and Bias is frustrating as you cannot launch your model or demonstrate the model’s skills unless the results are accurate.

Supervised Learning

The tradeoff between Bias vs. Variance is applicable only in supervised machine learning. Most importantly, you use these predictions in predictive modeling. This tradeoff will break the prediction error so you can analyze how your algorithm is performing.

Every machine learning model includes an algorithm that you train with the help of relevant data. The algorithm repeats the same model and enhances the model’s capability by making new data utilizing the training data.

There are various algorithms you can choose for your machine learning models. Some of the algorithms are:

  • Neural Networks
  • Decision Trees
  • SVM
  • Linear Regression

All the above algorithms are different than each other. The working style of the algorithm and how they process the data all differ. The quantity of Variance and Bias generate the most important difference between these algorithms.

Final Model

After you decide the algorithm and parameters you use for your project, you prepare your final model by inserting the data. You provide a lot of data to the machine learning model. Now you need to train those data sets and keep on testing until you start finding some results. The model will help in generating the prediction from previous data and develop new data.

Types of Prediction Error

The algorithm of the machine learning model will include these three types of prediction errors:

  • Variance
  • Bias
  • Irreducible Error

What is Bias?

The difference between the amount of target value and the model’s prediction is called Bias. You can change the Bias of a project by changing the algorithm or model. When the assumptions that you use in the model are simple, you will experience Bias.

You can derive the average value of the prediction by repeating the model’s building process and conducting the sampling process. You can extract resampling data from the model as it utilizes the training data set and generate accurate results. You can resample from various methods such as bootstrapping and K fold sampling.

When you resample the data, you are affecting the Bias. You will find a high level of Bias by measuring the difference between the sample data’s true values with the average prediction value. If a model is Bias, you will experience an underfitting model. Every model includes some bias.

You will find high Bias in a linear algorithm. That is why these algorithms boost the machine learning process. You will also find Bias in linear regression analysis due to a real-life problem that a simple model cannot help. You will find low Bias in the non-linear algorithm. A simple model has more Bias.

What is a Variance?

With Variance, you can find the target function’s quantity that you have to adjust if the algorithm is using different training sets. To keep it simple, you can say that a variance helps you understand the difference between random variables and expected values. Variance does not help you find the total accuracy, but you can find the model’s irregularity in using various predictions from different training data sets.

Variance can cause overfitting. In this condition, even the small variation will cause huge problems in the data set. When you have a model with high Variance, the data sets will generate random noise instead of the target function. Your model should have the capability to understand the difference between variables and input data of the result.

However, when a model has low Variance, the model’s prediction about the sample data is close. There would be a huge change in the target function’s projection during variance error.

If an algorithm has low Variance, you will experience logistic regression, linear regression, and linear discriminant analysis in the model. On the other side, with high Variance, you will experience k-nearest neighbors, decision trees, and support vector machines.

Irreducible Error

You cannot reduce the irreducible error or noise. This is the random data that the model utilizes for making the new prediction. You can consider this data as an incomplete feature set, mis-framed problem, or inherent randomness.

Why Bias and Variances are Essential

The machine learning algorithm you use for your project will utilize these statistical or mathematical models. Through these computations, it might develop two types of errors:

Reducible Error – You can minimize and control this error to enhance the outcome’s accuracy and efficiency.

Irreducible Error – These errors are natural, and you cannot remove these uncertainties.

You can reduce Bias and variances as these are reducible errors. To reduce these errors, you need to select a model having suitable flexibility and complexity. Furthermore, you can use suitable data for training the model and reduce these errors. This will help you in bringing the accuracy in the model.


Bias and Variance are the essential elements of machine learning that you should learn and understand. You need to use these components in supervised machine learning. In supervised machine learning, the algorithm learns through the training data set and generates new ideas and data. You need to maintain the balance of Bias vs. Variance, helping you develop a machine learning model that yields accurate data results.

No matter what algorithm you use to develop a model, you will initially find Variance and Bias. When you change one component, it will affect the other. So you cannot reduce both the components to zero. If you do, it will raise other problems. That is why you need to use a bias vs. variance tradeoff. To design an errorless model, you need to make both of these components prominent.


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