Year	gross (GPI)
1971	0.685509979724884
1972	0.664799988269806
1973	0.73183000087738
1974	0.79601001739502
1975	0.837109982967377
1976	0.900420010089874
1977	0.941630005836487
1978	0.967079997062683
1979	0.988510012626648
1980	0.977590024471283
1981	0.956139981746674
1982	0.95591002702713
1983	0.954850018024445
1984	0.954509973526001
1985	0.953130006790161
1986	0.969089984893799
1987	0.958440005779266
1988	0.94853001832962
1989	0.946569979190826
1990	0.951390027999878
1991	0.961560010910034
1992	0.970030009746552
1993	0.985319972038269
1994	0.983009994029999
1995	0.979330003261566
1996	0.986679971218109
1997	0.981519997119904
1998	0.990180015563965
2007	1.0095499753952
2012	1.01857995986938
2013	1.02781999111176
2014	1.01874005794525
2015	1.00173997879028
2016	0.96451997756958
2017	0.980929970741272
2019	1.00198996067047
2020	1.00943005084991