Hi Statalisters

I want to examine the effect of an intervention at different follow-up points. I'm using the difference-in-difference (DID) design to evaluate an intervention. My main DID-analyses use the common binary pre-post variable, but I'm also interested in effects at different follow-up periods. I've searched for ways of specifying different follow-up periods but have not found any concrete descriptions with quarterly data (although the command -ddid- may be a solution).

I'm thinking the following approach may do the trick, although I'm uncertain as I've not seen any other applications:
Code:
* Effect at 6 month follow-up (2Q)
gen byte post_6m = quarter >= tq(2016q3) & quarter <= tq(2016q4) 
* Effect at 12 months follow-up (4Q)
gen byte post_12m = quarter >= tq(2016q3) & quarter <= tq(2017q3)
* Effect (full follow-up)
gen byte post_16Q3 = quarter >= tq(2016q3)
xtreg suicideRate i.intervention##i.post_6m, fe
xtreg suicideRate i.intervention##i.post_12m, fe
xtreg suicideRate i.intervention##i.post_16Q3, fe
My aim with this is to estimate the ATET for follow-up periods using a post variable coded 0 for pretreatment quarters, 1 for 2 or 4 quarters (depending on 6 or 12 month follow-up), and then 0 again for the remaining follow-up period in the dataset (last time unit is 2017Q4).

Here is a data example:
Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input float(suicideRate intervention) byte(post_16Q3 post_6m post_12m) long region float quarter
 2.486646 0 0 0 0 1 211
 3.469676 0 0 0 0 1 214
2.0125837 0 1 0 1 1 230
 1.984417 1 0 0 0 2 210
 1.821562 0 0 0 0 3 209
3.2823925 1 0 0 0 4 210
 2.958134 1 0 0 0 4 213
2.2824166 1 0 0 0 4 218
2.0749242 1 0 0 0 4 219
3.4813704 1 0 0 0 4 220
 2.854724 1 0 0 0 4 222
 2.664677 1 1 1 1 4 226
 2.820055 1 0 0 0 6 212
 1.833036 1 0 0 0 6 213
1.3645698 1 0 0 0 6 219
end
format %tq quarter
label values intervention intervention
label def intervention 0 "Control", modify
label def intervention 1 "Intervention", modify
Hopefully someone has some input on this.

Best
Tarjei