Hi everyone,

I am trying to evaluate a policy that was implemented in 2007 in the US to stimulate research and development (R&D) for specific diseases. The policy was implemented in a staggered way: most diseases became eligible for the policy in 2007, but a few others became eligible in 2014, 2015, 2016 and 2018. My dependent variable is the sum of yearly trial registratrion per disease and registry. Since the policy targets a specific registry (ClinicalTrials.gov) and specific diseases, I isolate the impact of the policy using a triple difference approach. To do so, I use the below data and run the following specification:

Code:
egen regist_disease=concat(registry disease)
encode regist_disease, gen (registry_disease)
xtset registry_disease year

xtpoisson trials afterr##US##eligible afterr##US user_fee_lag1 dalys i.year, fe vce(robust)
margins afterr#US, dydx(eligible) pwcompare predict(nu0)
Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input float trials long registry str35 disease int year float(afterr US eligible user_fee_lag1 dalys after_user)
 0 10 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
10  5 "Ischemic heart disease" 2017 1 1 0 0 .08415308 1
 0 16 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
 0 18 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
 0  1 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
 0  2 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
 0 15 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
 0 17 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
 0 12 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
 2  3 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
 0  9 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
 0  4 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
 0 11 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
 0  7 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
 1  8 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
 0 14 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
 1  6 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
 0 13 "Ischemic heart disease" 2017 1 0 0 0 .08415308 1
 0  9 "Ischemic heart disease" 2012 1 0 0 0 .08102311 1
 0  1 "Ischemic heart disease" 2009 1 0 0 0 .07826114 0
 0 18 "Ischemic heart disease" 2019 1 0 0 0 .08481748 1
 0 14 "Ischemic heart disease" 2018 1 0 0 0 .08481748 1
 0 10 "Ischemic heart disease" 2006 0 0 0 0  .0758043 0
 2  6 "Ischemic heart disease" 2018 1 0 0 0 .08481748 1
 0  3 "Ischemic heart disease" 2011 1 0 0 0 .08027124 1
 0  2 "Ischemic heart disease" 2010 1 0 0 0 .07976772 0
 0 15 "Ischemic heart disease" 2006 0 0 0 0  .0758043 0
 0 13 "Ischemic heart disease" 2005 0 0 0 0 .07648688 0
 3  5 "Ischemic heart disease" 2012 1 1 0 0 .08102311 1
 0 17 "Ischemic heart disease" 2012 1 0 0 0 .08102311 1
 1  3 "Ischemic heart disease" 2018 1 0 0 0 .08481748 1
 0 13 "Ischemic heart disease" 2008 1 0 0 0 .07690977 0
 0  2 "Ischemic heart disease" 2013 1 0 0 0  .0814804 1
 0  2 "Ischemic heart disease" 2019 1 0 0 0 .08481748 1
 0 11 "Ischemic heart disease" 2006 0 0 0 0  .0758043 0
 0 17 "Ischemic heart disease" 2014 1 0 0 0 .08249104 1
 0 11 "Ischemic heart disease" 2016 1 0 0 0 .08412416 1
 0 18 "Ischemic heart disease" 2016 1 0 0 0 .08412416 1
 0  3 "Ischemic heart disease" 2016 1 0 0 0 .08412416 1
 2  6 "Ischemic heart disease" 2005 0 0 0 0 .07648688 0
 0 14 "Ischemic heart disease" 2016 1 0 0 0 .08412416 1
 0  7 "Ischemic heart disease" 2006 0 0 0 0  .0758043 0
 0  4 "Ischemic heart disease" 2016 1 0 0 0 .08412416 1
 0 17 "Ischemic heart disease" 2005 0 0 0 0 .07648688 0
 0  3 "Ischemic heart disease" 2005 0 0 0 0 .07648688 0
 0 15 "Ischemic heart disease" 2016 1 0 0 0 .08412416 1
 0 12 "Ischemic heart disease" 2015 1 0 0 0  .0837075 1
 0 15 "Ischemic heart disease" 2014 1 0 0 0 .08249104 1
 0 15 "Ischemic heart disease" 2015 1 0 0 0  .0837075 1
 0 11 "Ischemic heart disease" 2009 1 0 0 0 .07826114 0
 0  1 "Ischemic heart disease" 2012 1 0 0 0 .08102311 1
 6  5 "Ischemic heart disease" 2005 0 1 0 0 .07648688 0
 1  1 "Ischemic heart disease" 2006 0 0 0 0  .0758043 0
 0  9 "Ischemic heart disease" 2011 1 0 0 0 .08027124 1
 0  2 "Ischemic heart disease" 2009 1 0 0 0 .07826114 0
 0  4 "Ischemic heart disease" 2008 1 0 0 0 .07690977 0
 0  1 "Ischemic heart disease" 2015 1 0 0 0  .0837075 1
 0 10 "Ischemic heart disease" 2014 1 0 0 0 .08249104 1
 0  2 "Ischemic heart disease" 2018 1 0 0 0 .08481748 1
 0 13 "Ischemic heart disease" 2014 1 0 0 0 .08249104 1
 1  1 "Ischemic heart disease" 2010 1 0 0 0 .07976772 0
 2  1 "Ischemic heart disease" 2014 1 0 0 0 .08249104 1
 0 12 "Ischemic heart disease" 2012 1 0 0 0 .08102311 1
 0  9 "Ischemic heart disease" 2010 1 0 0 0 .07976772 0
 0  9 "Ischemic heart disease" 2018 1 0 0 0 .08481748 1
 0  4 "Ischemic heart disease" 2006 0 0 0 0  .0758043 0
 0  9 "Ischemic heart disease" 2019 1 0 0 0 .08481748 1
 0 17 "Ischemic heart disease" 2010 1 0 0 0 .07976772 0
 0  7 "Ischemic heart disease" 2008 1 0 0 0 .07690977 0
 9  5 "Ischemic heart disease" 2016 1 1 0 0 .08412416 1
 3  8 "Ischemic heart disease" 2014 1 0 0 0 .08249104 1
 0 16 "Ischemic heart disease" 2013 1 0 0 0  .0814804 1
 0 15 "Ischemic heart disease" 2018 1 0 0 0 .08481748 1
 0 18 "Ischemic heart disease" 2007 1 0 0 0   .075984 0
 0 11 "Ischemic heart disease" 2013 1 0 0 0  .0814804 1
 2  8 "Ischemic heart disease" 2012 1 0 0 0 .08102311 1
 2  1 "Ischemic heart disease" 2018 1 0 0 0 .08481748 1
 0 12 "Ischemic heart disease" 2018 1 0 0 0 .08481748 1
 0  7 "Ischemic heart disease" 2009 1 0 0 0 .07826114 0
 0 11 "Ischemic heart disease" 2010 1 0 0 0 .07976772 0
 0  8 "Ischemic heart disease" 2009 1 0 0 0 .07826114 0
 0 12 "Ischemic heart disease" 2008 1 0 0 0 .07690977 0
 0  1 "Ischemic heart disease" 2011 1 0 0 0 .08027124 1
 3  8 "Ischemic heart disease" 2018 1 0 0 0 .08481748 1
 0  3 "Ischemic heart disease" 2014 1 0 0 0 .08249104 1
 0 11 "Ischemic heart disease" 2019 1 0 0 0 .08481748 1
 1  8 "Ischemic heart disease" 2013 1 0 0 0  .0814804 1
 0  6 "Ischemic heart disease" 2016 1 0 0 0 .08412416 1
 0  7 "Ischemic heart disease" 2015 1 0 0 0  .0837075 1
 6  5 "Ischemic heart disease" 2011 1 1 0 0 .08027124 1
 0  1 "Ischemic heart disease" 2005 0 0 0 0 .07648688 0
 0  7 "Ischemic heart disease" 2014 1 0 0 0 .08249104 1
 0  4 "Ischemic heart disease" 2012 1 0 0 0 .08102311 1
 0  4 "Ischemic heart disease" 2005 0 0 0 0 .07648688 0
 0 17 "Ischemic heart disease" 2009 1 0 0 0 .07826114 0
 2  5 "Ischemic heart disease" 2006 0 1 0 0  .0758043 0
 0  7 "Ischemic heart disease" 2012 1 0 0 0 .08102311 1
 2  6 "Ischemic heart disease" 2015 1 0 0 0  .0837075 1
 1  6 "Ischemic heart disease" 2012 1 0 0 0 .08102311 1
 0  7 "Ischemic heart disease" 2019 1 0 0 0 .08481748 1
end
label values registry registry
label def registry 1 "ANZCTR", modify
label def registry 2 "CRIS", modify
label def registry 3 "CTRI", modify
label def registry 4 "ChiCTR", modify
label def registry 5 "ClinicalTrials.gov", modify
label def registry 6 "EU Clinical Trials Register", modify
label def registry 7 "German Clinical Trials Register", modify
label def registry 8 "IRCT", modify
label def registry 9 "ISRCTN", modify
label def registry 10 "JPRN", modify
label def registry 11 "LBCTR", modify
label def registry 12 "Netherlands Trial Register", modify
label def registry 13 "PACTR", modify
label def registry 14 "REBEC", modify
label def registry 15 "REPEC", modify
label def registry 16 "RPCEC", modify
label def registry 17 "SLCTR", modify
label def registry 18 "TCTR", modify
In 2011, a change was made to the policy with the implementation of a user fee: the policy was no longer free for companies to apply. The value of the user fee has been fluctuating annually since its implementation 2011. To control for this policy change within my policy, I initially included the variable user fee "user_fee_lag1" as a control variable in my regression. However, I have been told that it should be included as part of my policy variable. To do so, I have created a new after variable "after_user" that takes the value of 1 from 2011 onwards and I interacted it with the treated registry and diseases. Does this sound correct to you? Is it an issue if my two after variables ("afterr" and "after_user") overlap?

Code:
xtpoisson trials afterr##US##eligible afterr##US after_user##US##eligible dalys i.year, fe vce(robust)
Any help would be greatly appreciated! Thank you very much in advance!