What Does a Difs in Difs Estimate Actually Tell Us?

Most differences in differences papers these days have a treatment that turns on and/or off at different times. A specific group can be in the treated category or the control category depending on the year. What does this imply for our interpretation of a differences in differences estimate? Does this matter? Maybe not if a particular policy has one causal impact all the time, no matter what, but if the impact of a policy changes over time (and most things in life do change), then this matters. For a detailed and formal discussion of the issues, see Andrew Goodman-Bacon's NBER working paper, "Difference-in-Differences with Variation in Treatment Timing." For an easy (and fun!) to read explanation, see his twitter thread. 

For all authors of econometrics/econometrics-y papers, I'd love to read more twitter threads like Andrew's describing the main ideas of your work. And if you can insert a gif in between, that just makes everything more enjoyable. 

Cool Data Alert: Minimum Wages

Do you need to get started on your third year paper? Are you interested in studying the impacts of minimum wage changes? Well, have I got the data set for you! This data set tracks effective minimum wage rates across U.S. states from January 1, 2011 to January 1, 2018. Perhaps even cooler, the data set also contains information on the legislative histories behind each change (for example, when it was passed by the legislature and signed by the governor). For details, see this IZA Discussion Paper. Thank you, Michael R. Strain and coauthors, for putting this together.

 

Stata Trick: Are You Doing RD?

Then download this package and you'll have everything you need to do all of the analysis!

Stata Trick: Binscatter

Sure, tables, stars, and p-values are great and, for sure, important. But when do I really believe a set of results? When am I most likely to remember results? When there is a great picture! 

Great news: The Stata command, binscatter, makes it easy to make beautiful pictures of your regression results. Thank you, Michael Stepner for sharing the code! 

Click this link to learn how to make this: 

Asked to Referee a Paper a Second Time?

Sometimes there is a very clear referee for a paper. Maybe the author of the seminal paper on a (very particular, narrowly defined) topic. Maybe one of the few researchers who have used a certain data set extensively. Maybe something else. Anyway, when this happens, the same person will often be asked to referee the same paper multiple times. Actually, now that I think of it, I've even been asked to referee papers multiple times in cases with no overly obvious link to my research. What to do when you're asked to referee a paper a second time? I have always thought that there was a clear answer to this: Just tell the journal editor you have already refereed the paper for a different journal. In my experience, editors will still want to hear your thoughts on the paper, but maybe they will try to find additional referees as well. 

I never thought this was particularly controversial, but apparently it is! See this twitter thread for the controversy and this very thoughtful discussion of the issues written by Tatyana Deryugina.

The big take-aways: 

1. If an editor (knowingly) asks you to referee a paper a second time, then the first step is to check if the authors have changed the paper. Super convenient way to do this recommended by Tatyana: draftable.com.
2. If you are an author of a paper that was just rejected, please read the referee reports carefully and consider making any changes that will improve the paper--especially the low cost changes. At the very least, please fix typos! I spend a lot of time on referee reports. When I see that authors don't bother even fixing the typos, well, it feels..insulting. I try not to take this personally and just assume that the authors are in a time crunch, but this is probably not an ideal situation for anyone. I've also refereed papers that have changed quite dramatically (for the better!) after being a rejected at a different journal. Yes, this probably makes me look favorably at that particular submission, but perhaps even more importantly, the author gains my admiration in general. 

But speaking of peer review, have a look at what the wise folks at xkcd have come up with: 

Stata 15 Cheatsheets

Sure, Stata 15 is nice but what's even more exciting? Stata 15 cheatsheets!!! Download them! Print them! Post them! Memorize them! Use them!  

For Students Going on the Market: Time for the Big Push!

Ok, maybe asking for papers drafts is a special procrastination device of mine, but it's also really important. Here is some advice on twitter for students planning on going on the market. The big takeaway: "You should have a rough draft at this point, a good sense of what to do to polish everything up, and a plan with your advisors on how to do that. If you don't - make a final push or wait until next year."