## Introduction to Linear Regression

Linear regression is a statistical method that is commonly used to establish a relationship between two variables. In this method, one variable is considered the dependent variable while the other is considered the independent variable.

Linear regression is widely used in various fields, including economics, finance, medicine, and social sciences.

## Simple Linear Regression

Simple linear regression is a variant of linear regression in which only one independent variable is considered. The goal of simple linear regression is to develop a mathematical model that describes the linear relationship between the dependent variable and the independent variable.

In this method, the dependent variable is plotted on the Y-axis while the independent variable is plotted on the X-axis. The slope of the line of best fit that passes through the plotted data is calculated to determine the relationship between the variables.

## Multiple Linear Regression

Multiple linear regression is an extension of simple linear regression that takes into account more than one independent variable. In this method, a mathematical model is developed to describe the relationship between the dependent variable and multiple independent variables.

The goal of multiple linear regression is to determine the best fit line that can accurately predict the value of the dependent variable.

## Example with Full Dataset

To better understand the concepts of linear regression, let’s consider an example with a fictitious economy. Assume that the inflation rate is the dependent variable, while the unemployment rate, gross domestic product (GDP), and interest rate are the independent variables.

### Fictitious Economy Parameters

### The fictitious economy data will consist of 20 observations with the following parameters:

- The inflation rate ranges from 2% to 5%.
- The unemployment rate ranges from 6% to 8%.
- The GDP ranges from $50 billion to $70 billion.
- The interest rate ranges from 2% to 4%.

### Creation of Pandas DataFrame

To analyze the data, a Pandas DataFrame is created with the following code:

```
import pandas as pd
data = {'Inflation Rate': [2.0, 2.3, 2.5, 2.8, 3.0, 3.1, 3.5, 3.8, 4.0, 4.3, 4.5, 4.8, 5.0],
'Unemployment Rate': [6.0, 6.3, 6.5, 6.8, 7.0, 7.1, 7.5, 7.8, 8.0, 8.3, 8.5, 8.8, 9.0],
'Gross Domestic Product': [50, 53, 55, 58, 60, 61, 65, 68, 70, 73, 75, 78, 80],
'Interest Rate': [2.0, 2.3, 2.5, 2.8, 3.0, 3.1, 3.5, 3.8, 4.0, 4.3, 4.5, 4.8, 5.0]}
df = pd.DataFrame(data)
```

The code above creates a Pandas DataFrame with four columns: Inflation Rate, Unemployment Rate, Gross Domestic Product, and Interest Rate. The data in each column corresponds to the respective parameters of the fictitious economy.

### Displaying Full Dataset

Once the DataFrame is created, the data can be visualized with the following code:

`print(df)`

### Output:

```
Inflation Rate Unemployment Rate Gross Domestic Product Interest Rate
0 2.0 6.0 50 2.0
1 2.3 6.3 53 2.3
2 2.5 6.5 55 2.5
3 2.8 6.8 58 2.8
4 3.0 7.0 60 3.0
5 3.1 7.1 61 3.1
6 3.5 7.5 65 3.5
7 3.8 7.8 68 3.8
8 4.0 8.0 70 4.0
9 4.3 8.3 73 4.3
10 4.5 8.5 75 4.5
11 4.8 8.8 78 4.8
12 5.0 9.0 80 5.0
```

As seen above, the Pandas DataFrame displays the entire dataset, showing the values for each parameter. This enables analysts to easily view and manipulate the data.

## Conclusion

This article provided an overview of linear regression, including simple linear regression and multiple linear regression. An example of a fictitious economy was used to illustrate the application of linear regression, and we showed how to create a Pandas DataFrame to handle and display the data.

Now that you have a basic understanding of linear regression, you can apply this knowledge to real-world scenarios.

## Python Code for Linear Regression

Linear regression is a powerful tool for modeling relationships between variables. In this section, we will go through the python code required to perform linear regression.

This code can be used to establish a relationship between the dependent variable and the independent variables in your dataset.

### Importing Required Libraries

To perform a linear regression, various python libraries are required. We need to import them before proceeding with the analysis.

The libraries that are essential for this purpose are numpy, pandas, and sklearn. The import statement for these libraries are as follows:

```
import numpy as np
import pandas as pd
from sklearn.linear_model import LinearRegression
from sklearn.metrics import r2_score
```

### Arranging Independent and Dependent Variables

The next step is to arrange the dependent and independent variables in separate variables. The dependent variable is the variable that we want to predict or explain, while the independent variables are the variables that we use to predict or explain the dependent variable.

In our example, the dependent variable is the inflation rate, while the independent variables are the unemployment rate, GDP, and interest rate.

```
# Load the data into a pandas dataframe
df = pd.read_csv('data.csv')
# Define the dependent variable
Y = df['Inflation Rate']
# Define the independent variables
X = df[['Unemployment Rate', 'Gross Domestic Product', 'Interest Rate']]
```

### Transforming Independent Variables

Before performing linear regression, we need to transform the independent variables if they are not already normally distributed. We can use a logarithmic or square root transformation to normalize the data.

This can be done using numpy functions as follows:

```
# Transform the independent variables (log or square root transformation)
X_log = np.log(X)
X_sqrt = np.sqrt(X)
```

### Initializing and Fitting the Model

We can now initialize the model and fit the data to this model using the LinearRegression class. We will use the original independent variables for this example.

```
# Initialize the linear regression model
model = LinearRegression()
# Fit the model to the data
model.fit(X, Y)
```

### Generating Predictions

Once the data is fit to the model, we can generate predictions using the predict() function. This function takes in the same independent variables that we used to fit the model and returns predicted values for the dependent variable.

```
# Generate predictions on new data
new_data = [[7, 80, 3.5], [8, 85, 3.2]]
predictions = model.predict(new_data)
```

### Displaying Regression Results

Once the linear regression model is fit and predictions are made, we can display the regression results using the regressor’s coefficient values, constant coefficient, and standard errors. The regression results are available in the “model” object that we created earlier.

```
# Display model coefficients and constant
print("Model coefficients:", model.coef_)
print("Model constant (Y-intercept):", model.intercept_)
# Display standard error
print("Standard error:", np.sqrt(np.mean((Y - model.predict(X)) ** 2)))
# Calculate and display the adjusted R-squared
r_squared = model.score(X, Y)
n = len(df)
p = len(X.columns)
adjusted_r_squared = 1 - (1 - r_squared) * (n - 1) / (n - p - 1)
print("Adjusted R-squared: ", adjusted_r_squared)
```

### Interpretation of Regression Results

After generating regression results, the next step is to interpret these results. Some of the essential regression results that we should be aware of include adjusted R-squared, constant coefficient, independent variable coefficients, standard error, p-value, and confidence interval.

#### Adjusted R-squared

Adjusted R-squared measures the degree of variation in the dependent variable that is explained by the independent variables in the model. The adjusted R-squared increases when a new variable increases its explanatory power, making it an essential metric in evaluating model performance.

A higher adjusted R-squared value indicates a better model fit.

#### Constant Coefficient (Y-intercept)

The constant coefficient represents the predicted value of the dependent variable when all independent variables are zero. In terms of interpretation, if the independent variables in the model are larger than zero, then the constant coefficient is not directly meaningful.

#### Coefficients of Independent Variables

The coefficients of independent variables measure the effect that a change in the independent variable has on the dependent variable. Each coefficient reflects the change in the dependent variable with a one-unit change in the independent variable, holding all other independent variables constant.

A coefficient of zero indicates that the independent variable does not contribute to the model.

#### Standard Error

The standard error measures the degree of variation between the predicted values and the actual values. It is expressed in the unit of the dependent variable and provides insight into the spread of the data.

#### P-Value

The p-value measures the statistical significance of the coefficients. A p-value of less than 0.05 indicates that the coefficient is significant, and there is a high level of confidence in the effect of that variable on the dependent variable.

#### Confidence Interval

The confidence interval provides a range of values within which the true coefficient value is expected to lie. A 95% confidence interval represents a range of estimates that the true coefficient lies within 95% of the time.

## Conclusion

This article presented the Python code for linear regression, including the import of required libraries, arranging dependent and independent variables, transforming independent variables, initializing and fitting the model, generating predictions, and displaying regression results. Furthermore, we discussed the interpretation of regression results, including adjusted R-squared, constant coefficient, independent variables coefficients, standard error, p-value, and confidence interval.

By understanding these concepts and code, you can apply linear regression models in real-world scenarios and interpret the results to make informed decisions. Linear regression is a statistical method used to establish the relationship between a dependent variable and one or more independent variables.

Simple linear regression deals with a single independent variable, whereas multiple linear regression includes more than one independent variable. To perform linear regression, it is essential to import libraries such as numpy, pandas, and scikit-learn.

Before fitting the data to the model, we need to transform the independent variables, if necessary. Once the linear regression model is fit and predictions are made, we can interpret the results using various metrics, including adjusted R-squared, constant coefficient, independent variable coefficients, standard error, p-value, and confidence interval.

Overall, linear regression is a powerful tool with numerous applications in various fields, including economics and finance. It is important to understand the code required to perform a linear regression to use this method effectively.

By comprehending the results and interpretation of regression results, we can make informed decisions based on empirical data.