Year	gross (GPI)
1978	0.928780019283295
1979	0.937390029430389
1980	0.941340029239655
1981	0.942460000514984
1982	0.943560004234314
1983	0.945200026035309
1984	0.945360004901886
1985	0.947229981422424
1986	0.948920011520386
1987	0.953779995441437
1988	0.957589983940125
1989	0.963389992713928
1990	0.965449988842011
1991	0.969820022583008
1992	0.972379982471466
1993	0.955579996109009
1994	0.960979998111725
1995	0.963680028915405
1996	0.96806001663208
1998	0.956250011920929
1999	0.960879981517792
2000	0.967230021953583
2001	0.974749982357025
2002	0.971790015697479
2003	0.969969987869263
2004	0.964699983596802
2005	0.966939985752106
2006	0.967320024967194
2007	0.969760000705719
2008	0.972180008888245
2009	0.975220024585724
2010	0.981530010700226
2011	0.983799993991852
2012	0.983169972896576
2013	0.985319972038269
2015	0.979340016841888
2016	0.97613000869751
2017	0.973230004310608
2018	0.970459997653961
2019	0.968580007553101
2020	0.968540012836456