My dataset looks like this:
| Country | year | poverty rate | sales |
|---|---|---|---|
| Austria | 1950 | 0.54 | 142 |
| Austria | 1951 | 0.32 | 12441 |
| Austria | 1952 | 0.32 | 12441 |
| Bangladesh | 1950 | 0.11 | 142123123 |
| Bangladesh | 1951 | 0.52 | 1234 |
| Bangladesh | 1952 | 0.32 | 12441 |
| Sri Lanka | 1950 | 0.95 | 4215 |
| Sri Lanka | 1951 | 0.21 | 142421 |
| Sri Lanka | 1952 | 0.32 | 12441 |
I want to do tsset so that I can (for example) create a new variable for change in sales per year for each country. When I try to do tsset country year, I see "repeated time values within panel". How can I create a new variable that is change in sales per year for each country and year? I have more variables so I would want to be able to specify the variable.