Talk:Difference in differences

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Loose Thoughts?

The "Critics"-Section is a word by word copy of Betrand et al.... — Preceding unsigned comment added by 134.34.49.215 (talk) 11:44, 13 December 2011 (UTC)[reply]

let's get some explanation here: what is it!?!?

"Difference in differences" or "differences in differences"? Angrist and Pischke say the latter, as does the cited Bertrand et al. QJE article. — Preceding unsigned comment added by Spamdingel (talk • contribs) 18:03, 8 July 2011 (UTC) The blog post cited in the first footnote says "difference in difference". Who actually uses the phrase ("difference in differences") that is this entry's title? Spamdingel (talk) 18:06, 8 July 2011 (UTC)[reply]

I think there is no consensus on this, so I've added representative citations for each term in the first sentence.--Thosjleep (talk) 00:42, 13 December 2012 (UTC)[reply]

Removal or Change to Card and Krueger Example

I have issues with the way the Card and Krueger paper is used as an example. The way it is discussed focusses more on the results of the paper rather than using it as a pedagogical tool to discuss how diff-in-diffs work in practice. I also think it's a pretty bad paper, as evidenced by several criticisms (some discussion is here http://en.wikipedia.org/wiki/Minimum_wage#Card_and_Krueger). Therefore, it may not be the best paper to use as an example. It could be used as an example along with several other papers though. I think this would be better. It would highlight various types of diff-in-diffs papers from various disciplines. What does everyone else think? -PatrickButton (talk) 08:43, 5 April 2012 (UTC)[reply]

I was under the impression that Card & Krueger were the first economists to employ this method, so their paper would be relevant at least as the first example, even if the methodology isn't perfect. I agree that it should be a discussion of the economic procedure, and not of their results, so the in/validity of their results wouldn't be a factor in this article. --Docmcconl (talk) 11:23, 17 October 2012 (UTC)[reply]
I hope my rewritten version has solved this problem. --Masalih (talk) 20:36, 29 December 2012 (UTC)[reply]

Removing cleanup template

I'm removing the cleanup template, as it's unclear what is supposed to be cleaned up and I am not sure if there are fundamental problems with the article. Obviously, more can be done, but it doesn't seem to be an egregiously bad article.--Thosjleep (talk) 00:42, 13 December 2012 (UTC)[reply]

From Economists to Economists

This article seemed to have been written by an Economist, which per se is not something bad, to a readership of Economists, and this is bad.

Encyclopedia articles should be written with a general reader in mind, not a specialist, even if it is likely that the typical reader will end up being some specialists.

Until the Card and Krueger example, this article is incomprehensible to most readers who are not Economists, or who have not studied very advanced statistical methods.

Most of the article is technical and provides no intuition (in the same way of most Econometrics textbooks...), and when there is finally an example, this is presented in a sloppy way: that is FTE? What are the numbers in the table? What are the units of measurement in the table?

aw5678 at gmail dot com

More Theory - Fewer Examples

I made an attempt at a formal definition of DID. We should also add a section on estimation of errors. Furthermore, we should relate this article to other Wikipedia articles in econometrics (perhaps regression analysis?). One good example to illustrate the implementation of DID should be sufficient, and I think we should keep Card & Krueger's paper on unemployment because it is very famous and easy to relate to. Using more than one example is probably more confusing than helpful. If nobody protests, I would like to clarify and make the Card and Krueger example more neutral, and then remove the other example. --Masalih (talk) 17:20, 29 December 2012 (UTC)[reply]

Although it kinda hurts to remove someone's efforts, I have now removed the "Hypothetical Example" section. I incorporated some of the lessons there in the new implementation section. I also put the reference to the hypothetical example as an external link at the bottom. --Masalih (talk) 20:27, 29 December 2012 (UTC)[reply]

I added an assumptions section and removed the second paragraph in the introduction, which I think repeated the message of the first paragraph and stated the assumptions of the model. --Masalih (talk) 08:54, 30 December 2012 (UTC)[reply]

Cleaning the Math

I built on Masalik's contribution. If one thinks of how to carry this analysis using regression software, the rows (the observational units of the data) are indexed by the individual identifier $i$ , and the time $t$ only; the group membership would would be a column (a predictor), i.e.: its value would depend on the row, that is to say, would (clearly!) depend on $i,t$ .

I've used, without giving a formal definition, the notation $I(...)$ for the dummy variable that is 1 when (...) and 0 otherwise. I hope it is not confusing.

There remains to cover the case of multiple time periods before and after. — Preceding unsigned comment added by 10little (talk • contribs) 00:29, 25 August 2018 (UTC)[reply]

crappy article

cause it isn't written a the appropriate level wiki is supposed to be for the general reader; even the intro is full of jargon and isn't at all clear and sadly this is very typical of wiki now adays — Preceding unsigned comment added by 2601:192:4700:1F70:3D3D:8561:341E:76F4 (talk) 01:43, 10 August 2022 (UTC)[reply]

this article https://diff.healthpolicydatascience.org/

si about 100x better then the current wiki page the health policy article has less jargon and gives a clear simple explanation — Preceding unsigned comment added by 2601:192:4700:1F70:3D3D:8561:341E:76F4 (talk) 01:46, 10 August 2022 (UTC)[reply]

Parallel trend assumption is wrong in biology

For variables which have a natural zero (meaning negative measurements are impossible), which includes all measurements of temperature, mass, density, or activity (that is, essentially all measurements in biological applications), the parallel trend assumption is wrong, as it predicts negative measurements past some point in time. A better default assumption would be that, if the treatment has no effect, then a line drawn through the control group C's datapoints y = {C_{t = 0..n}}, and a line drawn through the treatment group T's datapoints y ={T_{t = 0..n}}, would meet at zero rather than at infinity. Philgoetz (talk) 18:01, 4 October 2024 (UTC)[reply]