make dummy =1 in year t to in year t-1

[Lucy Garcia]

Dear all,

I have a dummy variable, enact, which can only =1 once in the sample period. I want to create a "pseudo" dummy variable, enact1, which =1 in the year before the actual enact dummy =1. e.g., for firm 2, it has enact =1 in 2013, then enact1 should be =1 in 2012. I know this can be partly achieved by using the following code

bysort firm(year): gen enact1 = enact[_n+1]
replace enact1=0 if enact1==.

One problem with this code is, my sample period is 2010-2019, and some firms have less than 10 years of observation. If a firm has enact =1 in 2010, and 2010 is the first year of the sample period for that firm, then the code above won't create the enact1 dummy, because I don't have 2009 for that firm. I wonder what code could help to create the year t-1 first, and then code enact1 =1 for that year. Thanks a lot in advance for any help!

Som sample data

* Example generated by -dataex-. To install: ssc install dataex
clear
input byte firm float(year enact)
1 2010 1
1 2011 0
1 2012 0
1 2013 0
1 2014 0
1 2015 0
1 2016 0
1 2017 0
1 2018 0
1 2019 0
2 2010 0
2 2011 0
2 2012 0
2 2013 1
2 2014 0
2 2015 0
2 2016 0
2 2017 0
2 2018 0
2 2019 0
3 2014 1
3 2015 0
3 2016 0
3 2017 0
3 2018 0
3 2019 0
4 2011 1
4 2012 0
4 2013 0
4 2014 0
4 2015 0
4 2016 0
4 2017 0
4 2018 0
4 2019 0
end

[Nick Cox]

* Example generated by -dataex-. To install: ssc install dataex
clear
input byte firm float(year enact)
1 2010 1
1 2011 0
1 2012 0
1 2013 0
1 2014 0
1 2015 0
1 2016 0
1 2017 0
1 2018 0
1 2019 0
2 2010 0
2 2011 0
2 2012 0
2 2013 1
2 2014 0
2 2015 0
2 2016 0
2 2017 0
2 2018 0
2 2019 0
3 2014 1
3 2015 0
3 2016 0
3 2017 0
3 2018 0
3 2019 0
4 2011 1
4 2012 0
4 2013 0
4 2014 0
4 2015 0
4 2016 0
4 2017 0
4 2018 0
4 2019 0
end

bysort firm (year) : gen toexpand = cond(_n == 1, 2 * enact[1], 0)  
expand toexpand 
bysort firm (year) : replace year = year-1 if _n == 1 

list, sepby(firm)

     +--------------------------------+
     | firm   year   enact   toexpand |
     |--------------------------------|
  1. |    1   2009       1          2 |
  2. |    1   2010       1          2 |
  3. |    1   2011       0          0 |
  4. |    1   2012       0          0 |
  5. |    1   2013       0          0 |
  6. |    1   2014       0          0 |
  7. |    1   2015       0          0 |
  8. |    1   2016       0          0 |
  9. |    1   2017       0          0 |
 10. |    1   2018       0          0 |
 11. |    1   2019       0          0 |
     |--------------------------------|
 12. |    2   2009       0          0 |
 13. |    2   2011       0          0 |
 14. |    2   2012       0          0 |
 15. |    2   2013       1          0 |
 16. |    2   2014       0          0 |
 17. |    2   2015       0          0 |
 18. |    2   2016       0          0 |
 19. |    2   2017       0          0 |
 20. |    2   2018       0          0 |
 21. |    2   2019       0          0 |
     |--------------------------------|
 22. |    3   2013       1          2 |
 23. |    3   2014       1          2 |
 24. |    3   2015       0          0 |
 25. |    3   2016       0          0 |
 26. |    3   2017       0          0 |
 27. |    3   2018       0          0 |
 28. |    3   2019       0          0 |
     |--------------------------------|
 29. |    4   2010       1          2 |
 30. |    4   2011       1          2 |
 31. |    4   2012       0          0 |
 32. |    4   2013       0          0 |
 33. |    4   2014       0          0 |
 34. |    4   2015       0          0 |
 35. |    4   2016       0          0 |
 36. |    4   2017       0          0 |
 37. |    4   2018       0          0 |
 38. |    4   2019       0          0 |
     +--------------------------------+

[Lucy Garcia]

Hi Nick,
Thanks a lot, it works well!