Tag Archives: Reader Comments

OLS is between the effect on the treated and the effect on controls

We learn something new (and useful!) every day . . . Macartan Humphreys of Columbia University has shown why regression estimates of treatment effects can often be expected to fall between the average effect on the treated and the average effect on controls.   His theorem goes like this:  Let D denote treatment, let p(X) denote […]
Published June 4, 2009 | Tagged | Leave a comment

Comments on Bad Control

Derek Neal of the University of Chicago comments that our discussion of bad control in section 3.2.3 leaves the impression that more control is always better as long as the controls are pre-determined relative to the causal variable of interest. The leading counter-example is the case of within-family or twins estimates that we discuss as […]
Published May 8, 2009 | Tagged | 2 Comments