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# How to select the best regression techniques in machine learning?

• Bhumika Dutta
• Jul 28, 2022 Machine learning (ML) has a wide range of industrial applications in the majority of industries today, and as time goes on, all of these applications become more and more practical and efficient.

We're going to talk about regression in this article. On the target-predictor graph, regression displays a line or curve that passes through each data point in such a way that the vertical separation between the data points and the regression line is minimized.

Regression analysis is a supervised machine learning model that examines the relationship between the target or dependent variable and the independent variable in a dataset as predictive modeling. Let us start by understanding what regression analysis is, before delving into the techniques of regression.

## What is Regression Analysis?

A predictive modeling method called regression analysis examines the connection between a dependent and an independent variable(s). The dependent variable or target variable in a regression analysis is the key element that we wish to forecast or comprehend. The term "independent variable," sometimes known as a "predictor," refers to the elements that have an impact on the dependent variables or that are employed to forecast their values.

Forecasting, time series modeling, and determining the causal link between the variables are all done using this method. For data modeling and analysis, regression analysis is a crucial technique. Here, we attempt to minimize the discrepancies between the data points' varying distances from the curve or line by fitting a curve or line to them.

Regression is the ideal method for studying, for instance, the link between reckless driving and the number of accidents a driver causes on the road.

Usually, logistic and linear regression are the first topics people study in data science.

Let us understand regression analysis with an example:

Let's say that marketing firm A produces a variety of advertisements each year and generates revenue as a result. The following list displays the company's most recent five years' worth of advertisements together with the matching sales: Matching sales example (source)

The business now wants to run a \$200 advertisement in 2019 and is curious as to what sales projections are available. Regression analysis is therefore required to handle these kinds of prediction issues in machine learning.

## What is the importance of Regression Analysis?

The link between two or more variables is estimated through regression analysis. The regression analysis has a variety of advantages. These are what they are:

• It highlights the important connections between the dependent and independent variables.

• It shows the degree to which several independent factors influence a dependent variable.

We may examine the impacts of variables assessed on several scales using regression analysis, such as the impact of price adjustments and the volume of promotional activities. These advantages aid market researchers, data analysts, and data scientists in identifying and selecting the ideal collection of variables to use in predictive modeling.

## What are Regression Analysis Techniques?

To produce predictions, a variety of regression approaches are available. Three metrics primarily govern these methods:

• Number of Independent Variables

• Types of Dependent Variables

• The shape of the Regression line

Here are some of the commonly used regression techniques.

1. ### Linear Regression:

It is one of the most common regression techniques in machine learning. To forecast the output variables, a significant variable from the data set is selected. If the labels are continuous, such as the number of planes departing from an airport each day, etc., the linear regression technique is utilized.

The equation of linear regression is:

y = b*x + c;

where an is the intercept, b is the line's slope, and e is the error term, is how linear regression is represented. Based on the provided predictor variable, this equation may be used to forecast the value of the target variable (s).

'y' is the independent variable in the equation above, whereas 'x' is the dependent variable. The assumptions made by linear regression algorithms are that the relationship between the input and the output is linear. There will be a loss in output in a linear regression if the dependent and independent variables are not shown on the same line.

By utilizing a best-fit straight line, linear regression creates a link between the dependent variable and one or more independent variables (also known as the Regression line).

#### How to find the best fit line?

The Least Square Method makes quick work of this problem. It is the approach of fitting a regression line that is most frequently utilized. By reducing the sum of the squares of the vertical deviations between each data point and the line, it determines the line that best fits the observed data. There is no wiping out between positive and negative numbers since the deviations are squared before being combined.

1. ### Ridge Regression:

Another widely used linear regression approach in machine learning is ridge regression. A linear regression ML technique will be employed if just one independent variable is needed to predict the outcome. Since Ridge regression reduces the loss that is seen with linear regression, ML specialists favor it. In ridge regression, a ridge estimator predicts the output values in place of OLS (Ordinary Least Squares).

In ridge regression, the equation of linear regression is modified and the error term is removed through the shrinkage parameter (λ).

The equation for ridge regression will be:

L(x,y)= Min ( Σni=1 (yi - wixi)2 + λΣni=1 (wi)2)

Ridge Regression penalty is the name for the bias that is applied to the model. By adding the lambda to the squared weight of each distinct feature, we can calculate this penalty term.

High collinearity between the independent variables, which cannot be resolved by general linear or polynomial regression, is resolved using the shrinkage parameter. Regularization methods like ridge regression are employed to make the model less complicated. L2 regularization is another name for it.

1. ### Lasso Regression:

Least Absolute Shrinkage and Selection Operator, also known as Lasso is also another popular linear regression technique. Lasso penalizes the absolute magnitude of the regression coefficients like Ridge Regression. Additionally, it can increase the precision and decrease the variability of linear regression models.

By employing the shrinkage strategy, the determination coefficients in lasso regression are lowered near zero. To make the regression coefficients completely fit with different datasets, lasso regression is used to decrease them. Lasso regression is distinct from ridge regression in that it substitutes absolute values for squares in the penalty function.

The equation of Lasso regression is as follows:

L(x,y)= Min ( Σni=1 (yi - wixi)2 + λΣni=1 |wi|)

It can reduce the slope to zero since it uses absolute numbers, whereas Ridge Regression can only reduce it to a point close to zero. The estimations increase smaller and smaller until they reach zero, the more the penalty applies.

When a dataset has a lot of multicollinearity, ML professionals choose the lasso regression approach. A slight change in the data can have a significant impact on the regression coefficients due to the dataset's multicollinearity, which describes how closely connected the independent variables are to one another.

Applications for ML's Lasso method regression include forecasting and prediction. The lasso approach is also used in Data Mining for regression in addition to ML.

1. ### Logistic Regression:

The likelihood of an event being successful or unsuccessful is determined using logistic regression. When the dependent variable has a binary character (0, 1, True, False, or Yes/No), logistic regression should be used.

The equation of Logistic regression is as follows:

odds= p/ (1-p) = probability of event occurrence/probability of not event occurrence

ln(odds) = ln(p/(1-p))

logit(p) = ln(p/(1-p)) = b0+b1X1+b2X2+b3X3....+bkXk

It is an algorithm for predictive analysis that relies on the idea of probability. Although regression is a sort of analysis, the way that logistic regression is employed differs from that of the linear regression technique. The complicated cost function used in logistic regression is the sigmoid function or logistic function. In logistic regression, the data are modeled using this sigmoid function.

The function may be shown as follows:

f(x)= 1/(1+e-x)

Where f(x) is the output between the 0 and 1 value, x is the input to the function, and e is the base of the natural logarithm. The function returns the following S-curve when we give it the input values: Sigmoid Curve (source: javatpoint.com)

The idea of threshold levels is used; numbers over the threshold level are rounded to 1, while values below the threshold level are rounded to 0.

1. ### Stepwise Regression:

When working with several independent variables, we employ this type of regression. With the use of an automated procedure and with no human involvement, this approach chooses the independent variables.

This accomplishment is performed by identifying relevant variables by looking at statistical values like R-square, t-statistics, and AIC metrics. By adding or removing covariates one at a time depending on a predetermined criterion, stepwise regression essentially fits the regression model.

The following is a list of some of the most popular Stepwise regression techniques:

• Traditional stepwise regression accomplishes two tasks. For each phase, it adds or removes predictors as necessary.

• Forward selection begins with the model's most important predictor and gradually introduces more variables.

• Backward elimination starts with all model predictors and then eliminates the step's least significant variable.

• With the fewest possible predictor variables, this modeling approach seeks to optimize prediction accuracy. It is one way for dealing with data sets with larger dimensions.

1. ### Polynomial Regression:

If the power of the independent variable is more than 1, a regression equation is a polynomial regression equation. The best fit line in this regression method is not a straight line. Instead, it is a curve that matches the data points. Best fit line (source)

The equation of polynomial regression is as follows:

y= a+b*x2

It is often referred to as the special Multiple Linear Regression scenario in machine learning. The Multiple Linear Regression equation includes certain polynomial terms to convert them to polynomial regression. It is a linear model that has undergone modifications to increase precision.

The polynomial regression training dataset is non-linear. to fit the complex and non-linear functions and datasets. The original characteristics are converted into polynomial features with the necessary degree (2,3,...,n), and after that, a linear model is used to model them.

1. ### Gaussian Regression:

Due to the flexibility of their representations and built-in metrics of prediction uncertainty, Gaussian regression methods are often utilized in machine learning applications. Fundamental ideas like a multivariate normal distribution, non-parametric models, kernels, joint, and conditional probability serve as the foundation for a Gaussian process. Using prior information (kernels), a Gaussian processes regression (GPR) model may make predictions and offer uncertainty estimates for those predictions. It is a supervised learning technique created by the statistics and computer science sectors.

## How to select the best regression technique?

It is vital to select the optimal approach among the several regression models depending on the kind of independent and dependent variables, the dimensionality of the data, and other significant data properties.

Here are some elements to consider while selecting the best regression model:

1. ### Data Exploration:

Building a predictive model inevitably involves data investigation. Identifying the link and influence of the variables should be your first step before choosing the appropriate model.

1. ### Studying the Metrics:

We may examine many metrics, such as the statistical significance of parameters, R-square, Adjusted r-square, AIC, BIC, and the error term, to assess the goodness of fit for various models.

1. ### Cross-Validation:

The best method for assessing prediction models is cross-validation. Your data set is split into two groups here (train and validate). You may determine the prediction accuracy by looking at the simple mean squared difference between the observed and anticipated numbers.

1. ### Choosing model according to data:

You shouldn't utilize the automated model selection approach if your data set has a lot of confounding factors since you don't want to include them all at once in a model.

1. ### Goals of the project:

Additionally, it will depend on your goal. A weaker model might be simpler to use than one with great statistical significance.

1. ### The dimensionality of the data:

When the variables in the data set are highly dimensional and multicollinear, regression regularization techniques such as Lasso, Ridge, and ElasticNet function effectively.

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