The Phantom Menace of Omitted Variables - A Comment
This note demonstrates that in applied regression analysis, the variance of a coefficient of interest may decrease from the inclusion of a control variable, contrasting with Clarke's assertion (2005, 2009) that the variance can only increase or stay the same. Practitioners may thus be well-advised to include a relevant control variable on this basis alone, particularly when it is weakly correlated with the variable of interest.