Year	gross (GPI)
1970	0.970899999141693
1971	0.971700012683868
1972	0.971040010452271
1973	0.974020004272461
1974	0.971819996833801
1975	0.979359984397888
1976	0.981299996376038
1977	0.981599986553192
1978	0.982339978218079
1979	0.983060002326965
1980	0.984920024871826
1981	0.992540001869202
1982	0.988889992237091
1983	0.993669986724854
1984	0.992640018463135
1985	0.992869973182678
1986	0.994270026683807
1987	0.994700014591217
1988	0.99370002746582
1989	0.990069985389709
1990	0.989849984645844
1991	0.992030024528503
1992	0.994350016117096
1993	0.990369975566864
1994	0.988120019435883
1995	0.98827999830246
1996	0.990989983081818
1997	0.990490019321442
1998	0.988070011138916
1999	0.985610008239746
2000	0.985859990119934
2001	0.981949985027313
2002	0.979229986667633
2003	0.976670026779175
2004	0.979770004749298
2005	0.980570018291473
2006	0.982230007648468
2007	0.98309999704361
2008	0.98565000295639
2009	0.986379981040955
2010	0.983870029449463
2011	0.982050001621246
2012	0.984549999237061
2013	0.992590010166168
2014	0.993089973926544
2015	0.992919981479645
2016	0.993439972400665
2017	0.987190008163452
2018	0.990840017795563
2019	0.989679992198944
2020	0.992850005626678