Year	gross (GPI)
1971	0.553489983081818
1972	0.477809995412827
1976	0.432660013437271
1977	0.300520002841949
1978	0.221599996089935
1979	0.191310003399849
1980	0.198760002851486
1981	0.241539999842644
1982	0.209969997406006
1983	0.245279997587204
1984	0.230580002069473
1985	0.270410001277924
1987	0.334080010652542
1988	0.344350010156631
1989	0.462480008602142
2000	0.537850022315979