For this exercise, open the database takehome DD$.$dta. This dataset describes an observational study with units $$i$$ entering a treatment at different moments in time $$t$,$ i$.$e$.,$ in a staggered setting. The aim is to estimate the treatment effect of an intervention $($the variable $$treatment$)$ on an outcome $$Y$.$ As the units entering the treatment at a given moment $($t$=$g$)$ might be selective and There is enough control variables to control for the difference in composition in a credible way, we want to implement a difference$-$ in$-$differences estimator, which can account for unobserved heterogeneity under the assumption of a parallel trend $($in the dataset the variable $$g$$ indicates the moment when an individual enters the treatment, $$g$=0$ for never treated$).$ Answer the following questions.

$1.$ Provide a table describing the staggered setting: How many never treated units do we have? How many treated units are there by the end of the data observational periods?