Hello everyone,

I have an outcome which I measure between two dates for three different cohorts. The treatment whose effect I want to measure is COVID-19.
My control group is observed in 2016 (t=0) and 2019 (t=1), my first treatment group is observed in 2017 (t=0) and 2020 (t=1), and my second control group in 2018 (t=0) and 2021 (t=1).

Group t=0 t=1
Control 2016 2019
Treated 1 2017 2020
Treated 2 2018 2021

I tried to apply a triple difference regression using the following code, but I seem to be specifying something wrong...

Code:
clear
set obs 9999
egen id = seq(), from(1) to(9999) block(1)
gen outcome = 1 + rnormal()
generate year=2016 if id<=3333
replace year=2017 if id>3333 & id <=6666
replace year=2018 if id>6666 & id <=9999
generate t=0
save samplet0, replace
replace year=2019 if id<=3333
replace year=2020 if id>3333 & id <=6666
replace year=2021 if id>6666 & id <=9999
replace t=1
append using samplet0
generate treated1=0
replace treated1=1 if year==2020
generate treated2=0
replace treated2=1 if year==2021

reg outcome t##treated1##treated2
Does anyone have an idea? Thank you in advance!