<p>&quot;unrestricted treatment effect heterogeneity&quot; means the effect of treatment can differ for each individual, and there are no assumptions or limitations on how the effect differs.</p>
<p>Diff-in-diff models using twoway fixed effects with heterogeneous treatment effects and heterogeneous treatment times are known to be biased. <a href="https://www.sciencedirect.com/science/article/pii/S030440762030378X" rel="nofollow noreferrer">Sun and Abraham 2020</a> is a major reference.</p>
<p>This idea has very recently become a hot topic in econometrics. While I haven't read the paper you cite, it appears to be pushing this idea forward even more.</p>

CC BY-SA 4.0
2021-09-16T09:49:48.340Z
@Micheal , exactly this idea, it is mainly about the heterogeneous treatment onset. Just the language confuses me a little bit. Thanks a heap
Phil Nguyen
CC BY-SA 4.0
2021-09-16T09:52:29.650Z
I think "Diff-in-diff models using twoway fixed effects with heterogeneous treatment effects and heterogeneous treatment times are known to be biased" should be " "Diff-in-diff models using twoway fixed effects with **homogeneous** treatment effects and heterogeneous treatment times are known to be biased". Is it correct?
Phil Nguyen
CC BY-SA 4.0
2021-09-16T10:00:32.583Z
I don't think so. I think if treatment effects are homogeneous, then things are fine. The Sun and Abraham results (theorem 3) would imply this. There is of course a chance I am unaware of something.
Michael Gmeiner
CC BY-SA 4.0
2021-09-16T10:01:53.910Z
Ah yeah, it is what I mean, if the treatment effect is homogeneous (very rare case), things are fine. I may mistranslate your words.
Phil Nguyen
CC BY-SA 4.0
2021-09-16T08:59:54.137Z
2021-09-16T08:59:54.137Z
Michael Gmeiner
<p><a href="https://www.mendeley.com/catalogue/b1e55330-f605-363c-b07f-3ab67325e929/?utm_source=desktop&amp;utm_medium=1.19.8&amp;utm_campaign=open_catalog&amp;userDocumentId=%7B47d22c8f-e7ba-3ead-9833-eeae8a94d5f0%7D" rel="nofollow noreferrer">Borusyak, 2021</a> has a sentence</p>
<blockquote>
<p>We show that this estimator takes a particularly transparent form
<strong>under unrestricted treatment effect heterogeneity</strong>, while our
construction also yields efficiency when some restrictions on
treatment effects are imposed.</p>
</blockquote>
<p>I am wondering what does <strong>under unrestricted treatment effect heterogeneity</strong> mean? I translate it to that &quot;<strong>when the treatment effect heterogeneity is not restricted</strong>&quot;, and it also means that this situation works in both cases &quot;<strong>treatment effect heterogeneity</strong>&quot; and &quot;<strong>treatment effect homogeneity</strong>&quot;. Is it a correct thought?</p>
<p>I did <a href="https://ell.stackexchange.com/questions/297815/what-does-unrestricted-treatment-effect-heterogeneity-mean/297819#297819">ask this in the English Learner</a> but they said this content is beyond the English language question.</p>
<p>The answer from English learner's expert is</p>
<blockquote>
<p>However, I am more inclined to interpret it as &quot;the transparency of
our estimator when there are no restrictions is greater than the
transparency of other people's estimator when there are no
restrictions&quot; and &quot;the efficiency of our construction when there are
restrictions is greater than the efficiency of other people's
construction when there are restrictions.&quot;</p>
</blockquote>

<econometrics><nonexpert>
What does "unrestricted treatment effect heterogeneity" mean?
Phil Nguyen
# What does "unrestricted treatment effect heterogeneity" mean?

(Asked by: username_0 on 2021-09-16)

[Borusyak, 2021](https://www.mendeley.com/catalogue/b1e55330-f605-363c-b07f-3ab67325e929/?utm_source=desktop&utm_medium=1.19.8&utm_campaign=open_catalog&userDocumentId=%7B47d22c8f-e7ba-3ead-9833-eeae8a94d5f0%7D) has a sentence

> We show that this estimator takes a particularly transparent form
> **under unrestricted treatment effect heterogeneity**, while our
> construction also yields efficiency when some restrictions on
> treatment effects are imposed.

I am wondering what does **under unrestricted treatment effect heterogeneity** mean? I translate it to that "**when the treatment effect heterogeneity is not restricted**", and it also means that this situation works in both cases "**treatment effect heterogeneity**" and "**treatment effect homogeneity**". Is it a correct thought?

I did [ask this in the English Learner](https://ell.stackexchange.com/questions/297815/what-does-unrestricted-treatment-effect-heterogeneity-mean/297819#297819) but they said this content is beyond the English language question.

The answer from English learner's expert is

> However, I am more inclined to interpret it as "the transparency of
> our estimator when there are no restrictions is greater than the
> transparency of other people's estimator when there are no
> restrictions" and "the efficiency of our construction when there are
> restrictions is greater than the efficiency of other people's
> construction when there are restrictions."

**Tags:** econometrics, nonexpert

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## 1 answers

### Answer by username_1 on 2021-09-16. Score: 2 | Accepted answer

"unrestricted treatment effect heterogeneity" means the effect of treatment can differ for each individual, and there are no assumptions or limitations on how the effect differs.

Diff-in-diff models using twoway fixed effects with heterogeneous treatment effects and heterogeneous treatment times are known to be biased. [Sun and Abraham 2020](https://www.sciencedirect.com/science/article/pii/S030440762030378X) is a major reference.

This idea has very recently become a hot topic in econometrics. While I haven't read the paper you cite, it appears to be pushing this idea forward even more.

> **Comments:**
> **username_0**: @Micheal , exactly this idea, it is mainly about the heterogeneous treatment onset. Just the language confuses me a little bit. Thanks a heap  
> **username_0**: I think "Diff-in-diff models using twoway fixed effects with heterogeneous treatment effects and heterogeneous treatment times are known to be biased" should be " "Diff-in-diff models using twoway fixed effects with **homogeneous** treatment effects and heterogeneous treatment times are known to be biased". Is it correct?  
> **username_1**: I don't think so. I think if treatment effects are homogeneous, then things are fine. The Sun and Abraham results (theorem 3) would imply this. There is of course a chance I am unaware of something.  
> **username_0**: Ah yeah, it is what I mean, if the treatment effect is homogeneous (very rare case), things are fine. I may mistranslate your words.  

---

