Year	gross (GPI)
1981	0.963240027427673
1982	0.966090023517609
1983	0.968169987201691
1984	0.969219982624054
1985	0.970409989356995
1986	0.971010029315948
1987	0.97122997045517
1988	0.971840023994446
1989	0.972029983997345
1990	0.973010003566742
1991	0.974129974842072
1992	0.975040018558502
1993	0.974009990692139
1994	0.975329995155334
1995	0.974309980869293
1996	0.974500000476837
1997	0.974579989910126
1998	0.970579981803894
1999	0.967299997806549
2000	0.9685999751091
2001	0.964129984378815
2002	0.962670028209686
2003	0.959550023078918
2004	0.965740025043488
2005	0.966849982738495
2006	0.970650017261505
2007	0.972259998321533
2008	0.97613000869751
2009	0.981689989566803
2010	0.980989992618561
2011	0.980499982833862
2012	0.984830021858215
2013	0.986599981784821
2014	0.987999975681305
2015	0.988870024681091
2016	0.989790022373199
2017	0.983699977397919
2018	0.986389994621277
2019	0.985029995441437
2020	0.986630022525787