A Crash Course in Good and Bad Controls

Many students of statistics and econometrics express frustration with the way a problem known as “bad control” is treated in the traditional literature. The issue arises when the addition of a variable to a regression equation produces an unintended discrepancy between the regression coefficient and the effect that the coefficient is intended to represent. Avoiding such discrepancies presents a challenge to all analysts in the data intensive sciences. This note describes graphical tools for understanding, visualizing, and resolving the problem through a series of illustrative examples. By making this “crash course” accessible to instructors and practitioners, we hope to avail these tools to a broader community…

• NS
  National Science Foundation

  Award: #IIS-2106908
• TR
  Toyota Research Institute, North America

  Award: PO000897
• OO
  Office of Naval Research

  Awards: #N00014-17-S-1209, #N00014-21-1-235