Data from https://gks.ru/
## year diff_pers
## 1 2009 -2.940
## 2 2015 -13.367
## 3 2021 -4.249
## year diff_pers
## 1 2009 -10.951
## 2 2015 -13.367
## 3 2021 -5.154
## year diff_pers
## 1 2009 -4.8916
## 2 2015 -13.3674
## 3 2021 -0.8352