Year	gross (GPI)
1971	0.98717999458313
1972	0.993629992008209
1973	0.995199978351593
1974	0.998719990253448
1975	1.00657999515533
1976	0.977800011634827
1977	0.995360016822815
1978	0.979290008544922
1979	0.976689994335175
1980	0.978579998016357
1981	0.991199970245361
1982	0.993239998817444
1983	0.993189990520477
1984	0.995329976081848
1985	0.99456000328064
1986	0.995199978351593
1987	0.993650019168854
1988	0.994740009307861
1989	0.992780029773712
1990	0.996969997882843
1991	1.00211000442505
1992	1.00460994243622
1993	0.999580025672913
1994	0.997189998626709
1995	0.999100029468536
1996	0.993340015411377
1997	0.998440027236938
1998	0.98633998632431
1999	0.98351001739502
2000	0.9792600274086
2001	0.978680014610291
2002	0.976580023765564
2003	0.975799977779388
2004	0.961149990558624
2005	0.95907998085022
2006	0.96204000711441
2007	0.961210012435913
2008	0.969229996204376
2009	0.966369986534119
2010	0.957560002803802
2011	0.952620029449463
2012	0.958729982376099
2013	0.955229997634888
2014	0.965780019760132
2015	0.96806001663208
2016	0.969309985637665
2017	0.973469972610474
2018	0.967760026454926
2019	0.981689989566803
2020	0.978070020675659