panel data

[Adrienne Wold]

Hi,
I am working with panel data and have a binary treatment variable. I want to see how many units are in the "always control" category (treatment=0 for all years) but not sure how to approach this, as

codebook id if treatment=0

will return ID values that have 0 values for treatment for some years even if not always control.

Thank you.

[Øyvind Snilsberg]

bys id: egen ever_treated = max(treatment)
codebook id if ever_treated == 0

[Carlo Lazzaro]

Adrienne:
another option may be:

. use "https://www.stata-press.com/data/r16/nlswork.dta"
(National Longitudinal Survey.  Young Women 14-26 years of age in 1968)

. bysort idcode: egen wanted2=count(nev_mar) if nev_mar==0


.