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From |
Jen Zhen <jenzhen99@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: Pooling several discontinuities: Use observations twice? |

Date |
Mon, 6 Dec 2010 20:17:53 +0100 |

Dear all, here's an interesting question: I have a setup in which the assigned treatment size increases (by different amounts) every 2 years of age. What I've done so far is to regress my outcome on the assigned treatment applicable to the respective age interval, while controlling for a spline in age. But I'm wondering what I would gain anything from somehow aligning all discontinuities, so that I could then do a more standard Regression Discontinuity Design? At least I could then plot the discontinuity in a more intuitive way. So I'm pondering how to best implement this. For simplicity, say I have 4 age intervals, with assignment jumps between intervals 1/2, 2/3 and 3/4. Then observations in brackets 1 and 4 will in any case be used only once. But I'm thinking that observations from brackets 2 and 3 can give me 2 pieces of information, namely once what it's like to be to the right of respectively the 1st and the 2nd threshold, and once what it's like to be to the right of respectively the 2nd and the 3rd threshold. So I'm thinking of giving each observation from those intermediate brackets a twin using the -expand- command, and then assign each first twin to the next trheshold to its left and each second twin to the next threshold to its right. Then I want to compute for each observation the distance to its repsective threshold, and then just run a single regression of my outcome on the assigned treatment (I don't observe actual treatments) along with a flexible function of the distance from the threshold. I'm wondering however whether and if so how I will need to adjust standard errors if I use many observations twice, to make sure I do not overstate the amount of information I have? Or would you counsel to use each observation from an intermediate bracket only once, assigning those left of the bracket's median to the left threshold, and those right of the median to the right threshold? Thanks and all best, JZ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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