# Tag Archives: Reader Comments

## Just a little off

Careful reader John Bullock writes: I think that there may be a small error on page 185 of Mostly Harmless Econometrics. It lies with the y-axes for the panels of Figure 4.5.1. Those panels are from pages 32-33 of Acemoglu and Angrist 2001 (http://www.nber.org/chapters/c11054.pdf), but in the Acemoglu-Angrist article, the y-axes range from -.03 to […]

## Random Thoughts

Lauren Jones from U Toronto asks I have a question about semantics. You use the word "random" to describe both the treatment assignment variables D in RCTs, and also to describe the outcome variables Y in regression analysis. "Random" means something different in the first application than in the second. Indeed, you explain that Y […]

Published February 13, 2015 | Also tagged Econometrics and other courses, Questions | Leave a comment

## MHE p. 13 t-stats

How many have asked, you ask? Too many! Here’s the data and a program to do ’em. http://economics.mit.edu/faculty/angrist/data1/mhe/mhe

## regression: BLP not BLUE!

Scott Cunningham asks a big picture question regarding pedagogy in MHE: In chapter 3, you emphasize early on the important property of prediction. For example, Theorem 3.1.2 and 3.1.5. In my econometrics training years ago, early initiation into regression focused more on OLS as BLUE than as BLP (best linear predictor). I was curious why, […]

Published January 24, 2015 | Also tagged Econometrics and other courses, Questions | Leave a comment

## LDV, two ways

Celia writes: I have a question about including LDV in a model with FE. Will the problem of inconsistent estimates also arise if my DV is measured in year t+3 while my LDV is measured--for economic reasons--in year t-3? My guess is that it would only be problematic if the LDV was measured in t+2. […]

## whoops

Eagle-eyed Robson Santos notes: In the last paragraph of p. 55, the expectations of $f_{i}(s−4)$ is taken and the expectation of $f_{i}(s−1)$ is not. The text reads: Conditional on $X_{i}$, the average causal effect of one-year increase in schooling is $E[f_{i}(s)−f_{i}(s−1)|X_{i}]$, while the average causal effect of a four-year increase in schooling is $E[f_{i}(s)−E[f_{i}(s−4)]|X_{i}]$ In […]

## Pop Quiz

Colin Vance asks: A brief question about statistical significance: taking a “population first” approach to econometrics, you note on page 36 that “the regression coefficients defined in this section are not estimators; rather, they are nonstochastic features of the joint distribution of dependent and independent variables.” You later imply on page 40 that the issue […]

## The Cosmic Allness of OVB

Michael Wolf from the University of Zurich asks the following brilliant OVB question: Say the long regression of interest is (1) yi =α+ρsi +γ1MOi +γ2IQi +vi . (1) Here, MO stands for motivation and IQ stands for intelligence. In your notation then, Ai = (MOi, IQi)′ and γ = (γ1, γ2)′. In practice, motivation and […]

## Perry Preschool Subjects are Ageless

Observant reader Oliver Jones noticed that the Perry subjects can not be age 27 in 1993, as we mistakenly implied on page 11. Rather, 1993 is the publication date of a study looking at the Perry subjects when they were 27.

## A Fundamentally Sensible Question