How to Use glm in R for Binary Logistic Regression with Confounders

Описание: Learn how to include multiple confounding variables in binary logistic regression using `glm` in R. This guide simplifies the process and offers practical coding solutions!
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This video is based on the question https://stackoverflow.com/q/64708978/ asked by the user 'Junghun Yoo' ( https://stackoverflow.com/u/12759470/ ) and on the answer https://stackoverflow.com/a/64709109/ provided by the user 'Gregor Thomas' ( https://stackoverflow.com/u/903061/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Binary Logistic Regression in R

Binary logistic regression is a powerful statistical tool used to analyze the relationship between a binary outcome variable (like success/failure or yes/no) and one or more predictor variables. When dealing with multiple predictor variables, including covariates or confounders, things can get a bit tricky.

If your dataset has a large number of exposure variables and you want to analyze the association between each of these variables and the outcome, you might need to repeat the analysis for each exposure variable while controlling for additional factors like age or BMI. This post will guide you through the process of setting up your logistic regression models correctly in R.

The Problem

You have a dataset containing more than 50 exposure variables and a total of 16,000 entries. You aim to analyze the association between these exposure variables and a binary outcome, but your initial approach to include confounders in the regression model didn't work as expected.

In your first attempt, you created two functions, Model1 and Model2, which were supposed to run the regression analysis, but Model2 failed when trying to include multiple covariates. The main issue stemmed from how you combined variable names in the reformulate function used in the glm call.

The Solution

Understanding reformulate()

The key to resolving your issue lies in the use of the reformulate() function. Here's how you can use it correctly:

Combine Variables Correctly: Instead of using the + operator to combine predictors, use the c() function to create a vector of variable names.

Correct Function Setup:

Here’s how you can adjust your original functions:

[[See Video to Reveal this Text or Code Snippet]]

Minor Adjustments

In Model2, you should ensure you are not including age and bmi in the setdiff() function call since you are already adding them in the model. Adapt your logic to exclude them explicitly:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By restructuring how you combine your predictors in the reformulate() function, you can successfully include both the exposure variables and the confounders in your logistic regression analysis. This approach allows for more rigorous analysis, controlling for the influence of additional covariates.

Armed with this knowledge, you can now confidently analyze the associations in your dataset, ensuring robust statistical conclusions! Always remember the distinction between using c() and + in reformulate() to avoid errors in your regression models.

Feel free to reach out with any questions or share your experiences in performing logistic regression in R. Happy coding!