Difference between previous period and current with panel set

[John Skinner]

Hi,

I have a panel which observes firms over a 7 year period from 2015 to 2021.
I want to create a new variable (EmployeeChange) which is the difference between that period and the last.

To give an example of what I want

Serial	Year	NumEmployee	EmployeeChange
1	2015	5	.
1	2016	10	5
1	2017	12	2
etc.

My code is as follows:

xtset Serial Year
bys Serial Year: gen EmployeeChange = NumEmployee[_n]-NumEmployee[_n-1]

However it doesn't do anything.

Any help much appreciated.

[Rich Goldstein]

if I understand you correctly, the problem is that in your "bys" statement, Year is not in parens and it needs to be; as currently written, and based on the minimal and unusable example (please read the FAQ), this will do nothing; see

help by

[John Skinner]

if I understand you correctly, the problem is that in your "bys" statement, Year is not in parens and it needs to be; as currently written, and based on the minimal and unusable example (please read the FAQ), this will do nothing; see

help by

Thanks for your help Rich, the parentheses worked perfectly.

[Nick Cox]

Given your xtset

gen wanted = D.NumEmployee

automatically works panelwise, is shorter, and is smarter about gaps.

clear 
input Serial    Year    NumEmployee    EmployeeChange
1    2015    5    .
1    2016    10    5
1    2017    12    2
end 

xtset Serial Year 
gen wanted = D.NumEmployee

list 

     +----------------------------------------------+
     | Serial   Year   NumEmp~e   Employ~e   wanted |
     |----------------------------------------------|
  1. |      1   2015          5          .        . |
  2. |      1   2016         10          5        5 |
  3. |      1   2017         12          2        2 |
     +----------------------------------------------+