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nickchk's profile
Nick HK
Nick HK
Nick HK
@nickchk

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Nick HK

@nickchk

I am an economics professor at @CSUF. Constantly seesawing on exactly how seriously to take this whole Twitter thing. I guess DM me with consulting jobs?

nickchk.com
Joined October 2010

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    Nick HK‏ @nickchk 26 Nov 2018

    I've been getting used to gganimate and thought it would be useful to put together some illustrations of what various causal inference methods *actually do to data* and how they work. Here, for example, is what it means to control for a (binary) variablepic.twitter.com/lmEvJSPQgY

    11:21 AM - 26 Nov 2018
    • 1,361 Retweets
    • 3,363 Likes
    • Data Science Plow Walter Wonkite christopherbare Amit Sharma Usman Khan Manu HappyLight carmen alvarez The MMATOB Guy
    45 replies 1,361 retweets 3,363 likes
      1. New conversation
      2. Nick HK‏ @nickchk 26 Nov 2018

        Here is how one version of matching workspic.twitter.com/HGYRSgG2KC

        3 replies 42 retweets 204 likes
        Show this thread
      3. Nick HK‏ @nickchk 26 Nov 2018

        Instrumental variables (the Wald estimator, to be specific)pic.twitter.com/DNaVftuXfp

        2 replies 41 retweets 200 likes
        Show this thread
      4. Nick HK‏ @nickchk 26 Nov 2018

        Fixed effects (really just the animation for controlling again, but with more categories)pic.twitter.com/O7O16U0Fjj

        1 reply 37 retweets 159 likes
        Show this thread
      5. Nick HK‏ @nickchk 26 Nov 2018

        Difference-in-differencespic.twitter.com/lgtw5Z7wYi

        10 replies 132 retweets 366 likes
        Show this thread
      6. Nick HK‏ @nickchk 26 Nov 2018

        And finally (a simplified version of) RDDpic.twitter.com/QcBQo0ZWbE

        4 replies 46 retweets 160 likes
        Show this thread
      7. Nick HK‏ @nickchk 26 Nov 2018

        This is for a class I'm designing on programming and causal inference (h/t @causalinf) designed to go BEFORE the rest of the econometrics sequence. The idea is teaching concepts before methods. Notice that none of these graphs use regression! It's not necessary!

        5 replies 11 retweets 220 likes
        Show this thread
      8. Nick HK‏ @nickchk 26 Nov 2018

        Here's a link to a page with these graphs alongside DAGs and more explanatory detail, if you want something to link your students to. Also if you have any ideas for other methods I should animate let me know. http://nickchk.com/causalgraphs.html …

        5 replies 47 retweets 292 likes
        Show this thread
      9. Nick HK‏ @nickchk 26 Nov 2018

        Code now available in a repo:https://github.com/NickCH-K/causalgraphs …

        14 replies 30 retweets 312 likes
        Show this thread
      10. Nick HK‏ @nickchk 29 Nov 2018

        Nick HK Retweeted Nick HK

        Update for anyone still looking at this version of the thread. New version of the thread is up, with slower graphs:https://twitter.com/nickchk/status/1068215492458905600 …

        Nick HK added,

        Nick HK @nickchk
        As requested, slower graphs! Also added a graph on collider bias, the webpage explanation helps there. These graphs are intended to show what standard causal inference methods actually *do* to data, and how they work. This is what controlling for a binary variable looks like: pic.twitter.com/dTZxqY5JxA
        Show this thread
        0 replies 7 retweets 20 likes
        Show this thread
      11. End of conversation
      1. New conversation
      2. mere_mortise‏ @mere_mortise 27 Nov 2018
        Replying to @nickchk

        When controlling for a continuous variable v, one would fit a linear with OLS (i.e. a normal distribution as error distribution model) as a function of v, and then normalize the predicted means by subtracting them for each value of v? Or would one rather discretize v?

        1 reply 0 retweets 0 likes
      3. Nick HK‏ @nickchk 27 Nov 2018
        Replying to @mere_mortise

        You'd fit a linear with OLS and subtract the predicted values (no need to normalize). Formally this is known as the Frisch-Waugh-Lovell theorem (which also generalizes to multiple controls) if you want to see more about the process

        1 reply 0 retweets 1 like
      4. mere_mortise‏ @mere_mortise 27 Nov 2018
        Replying to @nickchk

        Excuse my sloppiness; by normalization I was referring to zero-centering the means. However, wouldn't it also conceivable that v not only affects the mean, but also the dispersion? So one would fit and normalize the variances too. Is that commonly done?

        1 reply 0 retweets 0 likes
      5. Nick HK‏ @nickchk 27 Nov 2018
        Replying to @mere_mortise

        A correlation between a control variable and the variance of the error term is known as heteroskedasticity, and can be addressed in a few different ways, one of which is robust standard errors, which doesn't normalize variances exactly but you could make an analogy to that

        1 reply 0 retweets 0 likes
      6. mere_mortise‏ @mere_mortise 27 Nov 2018
        Replying to @nickchk

        Exactly what I was looking for! Coming from a ML angle, the problem of transforming pdfs for different settings of the control variable to the same pdf reminded me of (optimal) transport theory. It seems one should be able ot use CycleGAN to map all pdfs to one without data loss.

        1 reply 0 retweets 1 like
      7. mere_mortise‏ @mere_mortise 27 Nov 2018
        Replying to @mere_mortise @nickchk

        I mean sufficiently little data loss such that it is possible to map the data back based on the control variable.

        1 reply 0 retweets 0 likes
      8. Nick HK‏ @nickchk 27 Nov 2018
        Replying to @mere_mortise

        I think that would be possible as long as you held onto the predictive model used to adjust. You'd just adjust back.

        1 reply 0 retweets 0 likes
      9. mere_mortise‏ @mere_mortise 27 Nov 2018
        Replying to @nickchk

        Yes. CycleGAN is defined by a cycle consistency loss which enforces a bijection between multiple domains (in this case between different settings of the control var). Which points are mapped to one another seems ill-defined though, so not sure it would work well.

        0 replies 0 retweets 0 likes
      10. End of conversation
      1. New conversation
      2. Jess Rohmann‏ @JLRohmann 27 Nov 2018
        Replying to @nickchk @malco_barrett

        Phenomenal teaching tool! Would love to show these to students if ok. Thanks :)

        1 reply 0 retweets 3 likes
      3. Nick HK‏ @nickchk 27 Nov 2018
        Replying to @JLRohmann @malco_barrett

        Oh absolutely! That's what it's for

        0 replies 0 retweets 4 likes
      4. End of conversation
      1. New conversation
      2. Shikta Das, PhD‏ @shikta_das 27 Nov 2018
        Replying to @nickchk

        Can I please use the r code for teaching? I am developing an R visualization course for the summer term.

        1 reply 0 retweets 4 likes
      3. Nick HK‏ @nickchk 27 Nov 2018
        Replying to @shikta_das

        Absolutely! Go for it

        0 replies 0 retweets 3 likes
      4. End of conversation

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