Linear regression (2024)

Table of Contents
An example Minitab 19 R FAQs

An example

The data for this example comes from measurements made by the US Federal Trade Commission on 25 different varieties of cigarettes: tar, nicotine, and carbon monoxide content.These are substances that are considered hazardous.Here we are interested in predicting the carbon monoxide (mg) emitted from the tar (mg) and nicotine (g) content.The weight of the cigarette (g) was also measured and can be considered in the analysis.

In this example, we first consider simple linear regression where the outcome of interest, carbon monoxide content (mg) is predicted from one continuous explanatory variable.We provide three separate simple regression models, using each of tar content (mg), nicotine content (mg) and weight (g) as the explanatory variable.

We also consider multiple linear regression where carbon monoxide content (mg) is predicted from three continuous explanatory variables simultaneously: tar content (mg), nicotine content (mg) and weight (g).

As the carbon monoxide content is a quantitative variable, the methods of statistical inference that can be applied here usually found under labels such as “linear regression” or “linear model” in software menus or code.

An appropriate report of the analysis may include summary statistics and a graph showing the relationship between the outcome and the explanatory variables. The summary statistics for this type of analysis often include the means and standard deviations for each variable as well as their correlations.Some examples are provided below.

Linear regression (1)

Linear regression (2)

The report of the regression analysis should include the estimated effect of each explanatory variable – the regression slope or regression coefficient – with a 95% confidence interval, and a P-value.TheP-value is for a test of the null hypothesis that the true regression coefficient is zero.In the context of multiple linear regression, an overall test of the null hypothesis that all true regression coefficients are zero may also be reported. In some disciplines, the test statistic and degrees of freedom are reported with the P-value for the overall test.

Two tables are provided below, summarising the test statistics and providing the regression coefficients respectively.

Linear regression (3)

The regression coefficients indicate the predicted change in carbon monoxide content (mg) for a one point increase in the relevant explanatory variable. To interpret this appropriately, we need to consider the scale range of the explanatory variable; for nicotine content, for example, the scale range is about two, and an increase of one mg in nicotine content is a relatively large change on this scale.In contrast the scale range for tar content is about 30 mg.It is sometimes useful to use a linear rescaling of the explanatory variables based on a meaningful scale change.Tar content, for example, could be rescaled to 5mg units.

The multiple regression model illustrates how the adjustment for other explanatory variables can have a strong influence on the effect of a particular explanatory variable; consider the simple model using nicotine content and the effect of nicotine content in the multiple variable model.Why does this arise?Examine the table of summary statistics above, and strength of relationship between the three explanatory variables considered.

In the examples of the output for reporting the regression analysis provided below, the simple linear regression using tar content (mg) is provided along with the multiple regression results.The results for the other two simple linear regression models are not provided (for simplicity).

Minitab 19

The output from Minitab 19 relevant to reporting the regression is shown here.Results for the test statistics table are in green; results for the coefficients table are in red.

Predicting Carbon monoxide content from Tar content:

Linear regression (4)

Predicting Carbon monoxide content from Tar content, Nicotine content and Weight:

Linear regression (5)

R

The output in R is shown below; RMarkdown has been used to produce this output.Often the results provided by R need to be rounded. The relevant output is underlined in green and red.

Predicting Carbon monoxide content from Tar content:Linear regression (6)

Predicting Carbon monoxide content from Tar content, Nicotine content and Weight:Linear regression (7)

Reference for the data

Mendenhall and Sincich (1992), Statistics forEngineering and the Sciences (3rd ed.), New York: Dellen PublishingCo.

Linear regression (2024)

FAQs

What is a real life example of linear regression? ›

A simple linear regression real life example could mean you finding a relationship between the revenue and temperature, with a sample size for revenue as the dependent variable. In case of multiple variable regression, you can find the relationship between temperature, pricing and number of workers to the revenue.

What is linear regression in simple terms? ›

What is linear regression? Linear regression analysis is used to predict the value of a variable based on the value of another variable. The variable you want to predict is called the dependent variable. The variable you are using to predict the other variable's value is called the independent variable.

When should linear regression be used? ›

You can use linear regression when you want to predict a continuous dependent variable from a scale of values. Use logistic regression when you expect a binary outcome (for example, yes or no). Here are examples of linear regression: Predicting the height of an adult based on the mother's and father's height.

Is it easy to learn linear regression? ›

Simplicity and interpretability: It's a relatively easy concept to understand and apply. The resulting simple linear regression model is a straightforward equation that shows how one variable affects another. This makes it easier to explain and trust the results compared to more complex models.

What is a good example of linear regression? ›

We could use the equation to predict weight if we knew an individual's height. In this example, if an individual was 70 inches tall, we would predict his weight to be: Weight = 80 + 2 x (70) = 220 lbs. In this simple linear regression, we are examining the impact of one independent variable on the outcome.

Where is linear regression usually used? ›

The variables that are used for the prediction are called independent variables (predictors). Multiple linear regression is frequently used in empirical social research as well as in market research. In both areas it is of interest to find out what influence different factors have on a variable.

How to explain regression in layman terms? ›

Regression — as fancy as it sounds can be thought of as “relationship” between any two things. For example, imagine you stay on the ground and the temperature is 70°F. You start climbing a hill and as you climb, you realize that you are feeling colder and the temperature is dropping.

How do you explain linear regression to a child? ›

In more technical terms, we can say that linear regression helps us predict or estimate the value of one variable (like the crispiness of the bread) based on the value of another variable (such as the toasting time). This method is used to make informed predictions about one factor when we know the value of another.

Why do we need linear regression? ›

Scientists in many fields, including biology and the behavioral, environmental, and social sciences, use linear regression to conduct preliminary data analysis and predict future trends. Many data science methods, such as machine learning and artificial intelligence, use linear regression to solve complex problems.

When should you avoid linear regression? ›

[1] To recapitulate, first, the relationship between x and y should be linear. Second, all the observations in a sample must be independent of each other; thus, this method should not be used if the data include more than one observation on any individual.

When we Cannot use linear regression? ›

Linear regression is a statistical technique used to understand the relationship between two continuous variables by fitting a straight line to the data points. However, it's not suitable for classification tasks where the goal is to predict which category or class an observation belongs to.

What is the difference between correlation and regression? ›

Regression: Difference between Correlation and Regression. Correlation measures the degree of relationship between two variables. Regression is about how one variable affects the other. To find the numerical value that defines and shows the relationship between two variables.

What is an example of a linear regression in real life? ›

Medical researchers often use linear regression to understand the relationship between drug dosage and blood pressure of patients. For example, researchers might administer various dosages of a certain drug to patients and observe how their blood pressure responds.

What is the simplest explanation of linear regression? ›

Simple linear regression aims to find a linear relationship to describe the correlation between an independent and possibly dependent variable. The regression line can be used to predict or estimate missing values, this is known as interpolation.

What is a regression for dummies? ›

Regression is a statistical technique that relates a dependent variable to one or more independent variables. A regression model is able to show whether changes observed in the dependent variable are associated with changes in one or more of the independent variables.

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