What do the numbers indicate? Birth rate per capita? And are the arrows expressing ranges, or expressing changes from the beginning to the end of the decades? (

What do the numbers indicate? Birth rate per capita? And are the arrows expressing ranges, or expressing changes from the beginning to the end of the decades? (Or maybe those are equivalent in this case?) Also, for those who don't remember the official names: GDR = German Democratic Republic = East Germany FRG = Federal Republic of Germany = West Germany