This week, we’re going think about internal and external validity in study design. We’ll also think a bit about how statistical evidence can inform theory and vice versa! (Internal validity: does the study make sense on its own terms, i.e. is it a true statement about the sample it studies? External validity: can we generalize the results of the study beyond the sample it looks at?)
Discuss the following questions as a group. Professor Rao will visit each group to help clarify any questions you may have. We’re going to try something a bit different this time: rather than having a longer small-group discussion period and a short full-class discussion period, we’re going to do a random seminar for the big group time. To give you more time to read the article and formulate your own questions/thoughts, there are fewer questions than usual in the exercise here.
Each of you will be selected randomly, without replacement, to share your thoughts/questions from your small-group discussions for (up to) 2 minutes. You can use your time to share your thoughts and questions, respond to others, or both.
When your time is up, the alert will flash, and Professor Rao will say it’s time to move on. If we finish with time to spare, we can have a less-formal chat. You can skip your turn if you’d like by saying “skip”, and you can also finish early if you’d like.
We’re going to do something a bit differently this time. Rather than having all members of the group read the same articles, you’ll each read this article about bunching estimators for minimum wage effects by Arin Dube and coauthors. Then you’ll each choose to read sections of a different article from the following set:
Card and Krueger 1994, Minimum Wages and Employment : The OG minimum wage study. Read pages 1-3 (up to the marker for footnote 5), look at figure 1, then skim section VIII (Interpretation, beginning on page 19), and read the conclusion. (Don’t get hung up in section VIII (Interpretation) on bits that you don’t quite understand—just get a sense of how they discuss their findings in light of the existing theoretical models. I want you to get the flavor, not build a detailed understanding in the time we have here.)
Kuehn 2014, The Importance of Study Design in the Minimum-Wage Debate : A more recent summary of what we’ve learned about minimum wage study design. Read carefully the Executive summary, the Introduction, the first paragraph of “Two approaches to studying the minimum wage”, Which approach makes more sense? (skip “Potential signs of progress”), and “What do we need to keep in mind in applying research to policy?” (Skim over bits that you don’t fully follow—focus on getting a flavor of the reasoning for which approach is preferred and why, and for the caveats in generalizing.)
Make sure each article gets read. You should each read the bunching estimators piece and one of the other articles. The goal here is to learn from each other!