Dear Statalist Community,

I am experiencing studying the impact of the introduction of body cameras worn by police officers on the total number of violent crimes committed by officers to offenders. I am interested in demonstrating that the introduction od the body cam decreases the number of violent crimes.

I have a panel data with data from 2009 to 2017, obtained by merging 2 datasets, one of Cincinnati and one of Orlando. In Orlando, bodycam was introduced in Nov 2015, while in Cincinnati in Aug 2016. The treatment is the intro of the body cam, the treatment group is Orlando and the control group is Cincinnati. Three periods are relevant:
- period 0 (Jan 2009 - Oct 2015): the cities haven't introduced the bodycam yet (both groups were not treated);
- period 1 (Nov 2015 - Jul 2016): Orlando was treated, and Cincinnati was not;
- period 2 (Aug 2016 - Oct 2017): both were treated (body cam was compulsory in both cities).

The variables are:
Tot_incidents = tot number of violent crime per month
Tot_monthnum = from 1 (Jan 2009) to 106 (Oct 2017)
Body_cam = dummy that gives 1 if the city has introduced the body cam, 0 otherwise
After_Nov15 = dummy that gives 1 if Tot_monthnum>= 83 (Nov 2015), 0 otherwise
Body_cam*After_Nov15 = interaction term

The normal diff-in-diff is Tot_incidents= b0+b1*Body_cam+b2*After_Nov15+b3*Body_cam*After_No v15 + e. This does not consider period 2, where the bodycam was introduced in Cincinnati.

I want to do a staggered diff-in-diff, in order to analyse also period 2, and to see the effect when bodycam was introduced also in Cincinnati. I am trying with the code

xtreg Tot_incidents Body_cam i.Tot_monthnum, fe

but it does not work.

Do you have any suggestion? Does it mke sense to analyse also period 2?

Thanks a lot in advance!!