What Is Backward Elimination Technique In Machine Learning?

What Is Backward Elimination Technique in Multiple Linear Regression?

Multiple linear Regression is a standard statistical method used to assess the relationships between a dependent variable and a set of independent variables. In many cases, there are too many independent variables to include all of them in the regression model. In these situations, modelers can use a backward elimination process to iteratively remove the least important variables until only the most important ones remain.

Backward elimination is a simple and effective way to select a subset of variables for a linear regression model. It is easy to implement and can be automated. The backward elimination process begins by fitting a multiple linear regression model with all the independent variables. The variable with the highest p-value is removed from the model, and a new model fits. This process is repeated until all variables in the model have a p-value below some threshold, typically 0.05.

Forward Selection vs. Backward Elimination

In machine learning, there are two main methods for feature selection: forward selection and backward elimination. Both methods have pros and cons, and which one you use will ultimately depend on your specific data and goals.

Forward selection is a greedy algorithm that starts with an empty set of features and adds features one by one until the model performance reaches a peak. This method is simple and easy to implement but can be computationally expensive and may not find the optimal set of features.

Backward elimination is a more systematic approach that starts with a complete set of features and removes features one by one until the model performance reaches a peak. This method is more computationally efficient but may not find the optimal set of features either.

So which method should you use? Ultimately, it depends on your specific data and goals. If you have a large set of potential features and want to be more efficient with your feature selection, backward elimination would be a better approach.

How to Implement Backward Elimination With Examples

Backward elimination is a machine learning algorithm that helps you choose the essential features of your data. This algorithm gradually removes features that are not important until only the most essential features remain.

There are many ways to implement backward elimination, but one of the most common methods is to use a p-value threshold. P-values are a measure of how likely a feature is to be necessary. A p-value threshold is a p-value below which a feature will be removed.

For example, let's say you have a dataset with ten features. You decide to use a p-value threshold of 0.05. Any feature with a p-value greater than 0.05 will be removed.

To implement backward elimination, you first need to calculate the p-values of each feature. Then, you compare the p-values to your threshold and remove the features with p-values greater than the threshold.

You can continue to do this until all of the features have been removed, or you reach your desired number of features.

Let's take a look at an example. Say you have the following dataset:

In this dataset, we would remove feature_1 and feature_2 since they have p-values less than our threshold of 0.05. Feature_3 would be kept since its p-value is more significant than our threshold. This process will continue until all of the features have been removed or we reach our desired number of features.

Our Learners Also Ask

1. What is backward elimination in Regression?

Backward elimination is a method used in regression analysis to select a subset of explanatory variables for the model. The model includes the initial and all explanatory variables in backward elimination. Then, the variable with the highest p-value is removed from the model. This process is repeated until all variables in the model have a p-value below a given threshold. Backward elimination is an efficient way to build a regression model with a small number of explanatory variables.

2. What are backward elimination and forward selection?

Backward elimination and forward selection are methods used in feature selection, which is the process of choosing the most relevant features for a model. Backward elimination starts with all features included in the model and then removes the least relevant features one at a time. Forward selection starts with no features included in the model and then adds the most relevant features one at a time.

3. How do you do backward elimination in Python?

Python's `sklearn` library provides a handy function for backward elimination on a linear regression model. This function is called `backward_elimination()`.

You must first fit a linear regression model to your data to use this function. Then, you can pass the model into the `backward_elimination()` function along with a significance level (usually 0.05). The function will then remove the least significant predictor from the model until all predictors in the model are significant.

4. What are forward and backward Regression?

Forward Regression starts with all the potential predictor variables and removes the ones that are not statistically significant. This is done until only the significant predictors remain. Backward Regression, on the other hand, begins with all the predictor variables and removes the ones that are not statistically significant. This process is repeated until only the significant predictors remain.

5. How do you do a backward elimination in SPSS?

Backward elimination is a statistical method used to find the simplest model that explains the data. In SPSS, backward elimination can be used to find the best model by iteratively removing variables that are not statistically significant. 

To do a backward elimination in SPSS, select the variables you want to include in the model. Then, click on the Analyze tab and choose Regression. Next, select the variables you want to remove from the model and click on the Remove button. Finally, click on the Run button to see the model's results.

Conclusion

The backward elimination technique is a method used in machine learning to improve the accuracy of predictions. This method removes features that are not predictive of the target variable or not statistically significant. Backward elimination is a powerful technique that can improve the accuracy of predictions and help you build better machine learning models. Also, upskill yourself with our AI ML Certification.