Bivariate Linear Regression Analyses

#1
For a course, I need to superficially understand an applied statistical approach in a research paper. The research paper I chose is listed below, and utilizes a bivariate linear regression model in its analysis. I believe that the article is stating they utilized this regression model in order to narrow down various disease and treatment options that may be associated with diagnosed white matter abnormalities, before going on to utilize a multivariable linear regression model to evaluate overall significance. Through reading this article, do you believe I have the correct interpretation of the statistical method utilized in the study? Any feedback is welcome!
@hlsmith
 

hlsmith

Less is more. Stay pure. Stay poor.
#2
How were the variables formatted? This would help with understanding the use of the approach. Of note, this process of initially screening variables is common, but actually frowned upon. Variable selection should be based on context knowledge and the use of a direct acyclic graph. The issues being -looking at a variable all by itself does not allow the analyst to understand how it may covary in the presence of another variable. Drawing out their relationships allows the investigator to see if the variable may be a cause or effect of another variable, etc. -> prior to removing other model terms.