lagged variable 만들기

Create lag (or lead) variables using subscripts.

        . gen lag1 = x[_n-1]
        . gen lag2 = x[_n-2]
        . gen lead1 = x[_n+1]

You can create lag (or lead) variables for different subgroups using the by prefix. For example,

        . sort state year 
        . by state: gen lag1 = x[_n-1]

If there are gaps in your records and you only want to lag successive years, you can specify

        . sort state year
        . by state: gen lag1 = x[_n-1] if year==year[_n-1]+1

*  L. 과 [_n-1]의 차이점은 아래의 포스팅을 참조

https://www.statalist.org/forums/forum/general-stata-discussion/general/1582274-lagged-variables-difference-between-l-variable-and-variable-_n-1

lead variable을 만들고 싶을 때,   패널 데이터라면 

xtset pid wv 

gen income_f= F.income