Overfitting and Underfitting in Machine Learning

A model is said to be a robust machine learning model if it correctly generalizes any new input data from the problem domain. It lets us make assumptions about future data that the computer model has never seen before. To test how well a machine learning model learns and generalizes new data, we have overfitting and underfitting, mainly responsible for the lousy performance of machine learning algorithms. If you have an interest in underfitting and overfitting, machine learning for beginners can be an option for you. There are loads of machine learning certification courses online.


Knowledge of Blog

  • Underfitting
    • Detection of underfitting model
    • Techniques to reduce underfitting
  • Overfitting
    • Detection of an overfitting model
    • Methodologies to minimize overfitting
  • Conclusion


Let’s grasp two basic terms before diving further:

  • Bias: Assumptions that make the role more comfortable to understand.



  • Variance: If you train your data on training data and get a deficient error when you change the data and then prepare the same previous model, you experience a high failure, it’s referred to as variance.





A statistical model or machine learning algorithm is said to be inadequate when it can not catch the underlying course of the data. Underfitting slaughters the accuracy of our machine learning model. It merely implies that our model or algorithm does not match the data well enough. It usually happens when we have fewer data to build an accurate model, and when we try to develop a linear model with non-linear data. In such circumstances, the rules of the machine learning model are too easy and flexible to apply to such minimal data, and therefore the model is likely to make a lot of wrong predictions.


Detection of underfitting model

The model may under-fit the data, but it is necessary to know when to do so. The following measures are the tests that are used to determine whether or not the model is underfitting.

  • Training and Validation Loss

During training and validation, testing the loss caused by the model is necessary. If the layout is underfitting, the loss for both training and validation would be substantially higher.

  • Over Simplistic Prediction Graph


When a graph is plotted to show the data points, and the fitted curve, and the curve is over-simplistic, the model is under-fitting. A more complicated model needs to be carried out.

  • Classification

Many classes will be misclassified in the training set, as well as in the validation set. On data analysis, the graph would show that if there were a more complex model, more groups would have been correctly categorized.

  • Regression

The final “Best Match” line does not aptly suit the data points. When watching, it would appear like a more complex curve will suit the data better.


Techniques To Reduce Underfitting

In a nutshell, underfitting is high bias and low variance. Let us see a few methods for the reduction of underfitting.

  • Boost the sophistication of the model


  • Increase the number of features, conduct feature engineering


  • Remove the noise from the information.


  • Raise the number of epochs or increase the duration of training to achieve better results.





A mathematical model is said to be over-fitted when we train it with much data. Once a model is equipped with many results, it starts to learn from the noise and incorrect data entries in our data collection. The model does not pigeonhole the data correctly because of so much information and noise. The causes of over-fitting are non-parametric and non-linear methods because these types of machine learning algorithms have more freedom to build a dataset-based model and, therefore, can make unrealistic models. The approach to prevent overfitting is to use a linear algorithm if we have direct data or if we have a maximum depth of parameters if we have decision trees.


Detection of an Overfitting Model

The parameters to be used to determine whether or not the model is overfitting are identical to those of the underfitting model. These are given below:

  • Training and Validation Loss

 As already mentioned, it is essential to measure the model loss during training and validation. A shallow training loss but a high validation loss will suggest that the model is overfitting. In fact, in Deep Learning, if the training loss tends to decrease while the validation loss stays stagnating or begins to increase, it also means that the model is over-fitting.

  • Too Complex Prediction Graph

When a graph is plotted showing the data points, and the fitted curve and the curve is too complicated to be the simplest solution that matches the data points correctly, the model is overfitting.

  • Classification

When each class is appropriately categorized in a training set by creating a very complicated decision boundary, there is a strong probability that the model will be over-fitting.

  • Regression

If the final “Best Fit” line crosses every single data point by creating an unnecessarily complicated curve, the model is likely to be over-fitting.


Methodologies To Minimize Overfitting

Concisely, overfitting is a low bias and high variance. Let us see some methods to mitigate overfitting.

  1. Increase your training data.
  2. Reduce the complexity of the model.
  3. Fast stopping during the training process (have an eye on the loss during the training cycle as soon as the damage starts to increase the stop training).
  4. Ridge Regularisation and Lasso Regularisation
  5. Using the neural network dropout to fix overfitting.



Resolving the problem of bias and variation is only about coping with over-fitting and under-fitting. Bias is minimized, and the variance concerning the complexity of the model is increased. As more parameters are attached to the model, the complexity of the model increases and variance becomes our primary concern, while bias slowly decreases. Machine learning experts suggest that we do the proper study of our datasets before starting our project. Data science is a discipline that has a lot to learn and add to the world. The only obstacle is that one should be able to know more and give it back to society. Start your machine learning training journey now!


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