# When Should I Use Ensemble Methods?

Ensemble methods refer to a class of machine learning techniques that combine multiple models and take their average to produce a more robust and accurate prediction. This approach is often compared to the idea of “strength in numbers” or “two heads are better than one.” Ensemble methods help cover the shortcomings of base algorithms when dealing with diverse datasets. Ensemble methods in machine learning algorithms come in quite handy when dealing with:

• High variance or bias
• An overfitting algorithm
• Outliers in the dataset
• High noise in the dataset
• Improving overall prediction stability

## Ensemble Models – Why Do We Need Them?

Ensemble methods are becoming increasingly popular in the field of machine learning, resorting to base learners utilizing different algorithms working with diverse training datasets, ultimately leading to a robust classifier, hence improving predictability, accuracy, and variance. However, the question remains, in what scenarios should ensemble methods be utilized?

## High Variance in Data

When dealing with training datasets to be used in different machine-learning algorithms, we every so often confront high variance and high bias data. A high variance occurs when minor changes in the data significantly impact the model’s predictions, whereas a high bias occurs when the predicted values are substantially different from the actual values, ultimately leading to unrepresentative training data and sometimes overlooking regularities in the concerned dataset. Ensemble methods can address this by averaging the predictions of multiple models, creating a more accurate and stable prediction using the training data at hand.

For example, training three models on a set of data using input features produces an output. We train three models on this dataset: a linear regression model with low variance and high bias, a decision tree model with a high variance but low bias, and a support vector machine model with moderate bias and variance. They all have their strengths and weaknesses based on biases and variances. Utilizing ensemble methods, we can average the predictions of these models and get reliable results. Hence resulting in an effective way to balance the bias-variance trade-off.

## Reducing the Risk of Overfitting

Getting the required outcomes using the training set of data and inversely getting inaccurate or undesirable predictions using a new dataset can be termed overfitting. This can be addressed by using ensemble methods, i.e., using various models leading to a classifier. When several base algorithms are performing similarly in terms of prediction and accuracy using the test set of data, ensemble methods can drastically improve the final prediction by utilizing the result of several base algorithms.

Take an example of a certain machine learning algorithm, specifically linear and logistic regression tends to be greatly affected by the presence of outliers in the input dataset. Hence averaging the predictions of multiple similar result-producing algorithms models, one can also reduce the risk of overfitting, performing accurately on training as well as new data.

## Reducing Outliers

Abnormalities in the input dataset can cause the machine learning model to produce inaccurate and abnormal results, commonly termed outliers. Outliers can occur either naturally in the dataset or through some human error in measurement, ultimately affecting the critical statistical data. This can be tackled by either using a machine learning algorithm that is less sensitive to outliers, such as in Support Vector Machines, which can utilize the outlier detection technique or with the assistance of an ensemble method. One can drastically improve the accuracy of statistical data by using ensemble methods, i.e., averaging the results obtained from several algorithms hence, proving the reliability of the obtained result.

## Minimizing Noise in Data

When dealing with the presence of noise, i.e., unwanted behavior within the concerned data, whether in the form of feature set noise, incorrect collection from either humans or instruments or label noise, or mislabeled examples, it can ultimately result in undesirable predictions from the machine learning model. This can be addressed using an appropriate ensemble method, eventually minimizing the impact of a particularly noisy dataset.

One real-life example can be noisy data in financial fraud detection. Fraudulent transactions are often disguised and mixed with legitimate transactions, making it difficult for fraud detection models to identify them accurately. By using ensemble methods, one can train multiple models on different subsets of data using slight modifications, aggregating the predictions of each model to generate a final prediction.

## Improving Prediction Stability

When dealing with diverse sets of input data, predictions can significantly vary in contrast to the desired outcomes. Utilizing multiple algorithms will lead to diversified predictions, making the preferred outcome goal unsatisfactory. To deal with this, ensemble methods are used in which numerous models are taken advantage of, and their outcomes are averaged to produce a stable prediction by the use of a classifier.

For example, in the field of weather forecasting, ensemble methods can be utilized to improve prediction stability. Complex mathematical algorithms are used in weather forecasting algorithms to predict future weather conditions based on past weather data. However, weather data can be noisy and subject to variability, which can lead to unstable predictions. Ensemble methods are used by weather forecasters to combine the predictions of multiple weather models to overcome this issue. Each model may use different inputs or algorithms, which can lead to variations in the predictions. By combining the outputs of multiple models, weather forecasters can create a more stable and accurate prediction.

## Wrap Up

Ensemble methods are a valuable tool in the field of machine learning that can help improve prediction accuracy and stability. They are particularly useful when dealing with high variance or noisy data, reducing the risk of overfitting, minimizing the impact of outliers, and improving prediction stability.

Ensemble methods can be applied in various real-life scenarios, such as financial fraud detection and weather forecasting, where accurate and reliable predictions are critical. By leveraging the strengths of multiple algorithms, ensemble methods provide a powerful solution to many machine learning challenges.