Year	gross (GPI)
1971	0.939050018787384
1972	0.941569983959198
1973	0.944050014019012
1974	0.94498997926712
1975	0.946470022201538
1976	0.946749985218048
1977	0.947130024433136
1978	0.949339985847473
1979	0.95058000087738
1980	0.952690005302429
1981	0.954349994659424
1982	0.960619986057281
1983	0.964299976825714
1984	0.966880023479462
1985	0.970830023288727
1986	0.972880005836487
1987	0.972679972648621
1988	0.973819971084595
1989	0.974590003490448
1990	0.975340008735657
1991	0.976459980010986
1992	0.97749000787735
1993	0.980560004711151
1994	0.9791100025177
1995	0.97886997461319
1996	0.976249992847443
1997	0.974030017852783
1998	0.971780002117157
1999	0.972220003604889
2000	0.971560001373291
2001	0.974200010299683
2002	0.976400017738342
2003	0.980109989643097
2004	0.982630014419556
2005	0.983009994029999
2006	0.985909998416901
2007	0.987479984760284
2008	0.989160001277924
2009	0.991620004177094
2010	0.993990004062653
2011	0.995869994163513
2012	0.995280027389526
2013	0.99769002199173
2014	0.999440014362335
2015	0.999230027198792
2016	0.998749971389771
2017	0.996339976787567
2018	0.993369996547699
2019	0.993640005588531
2020	0.991580009460449