Year	gross (GPI)
1971	0.986119985580444
1972	0.990220010280609
1973	0.992039978504181
1974	0.992030024528503
1975	0.989799976348877
1976	0.994520008563995
1977	0.998340010643005
1978	0.997780025005341
1979	0.998170018196106
1980	0.993189990520477
1981	0.996020019054413
1982	1.00004994869232
1983	0.999599993228912
1984	0.998979985713959
1985	0.997229993343353
1986	0.996100008487701
1987	0.992129981517792
1988	0.991900026798248
1989	0.985790014266968
1990	0.981540024280548
1991	0.979470014572144
1992	0.977689981460571
1993	0.980440020561218
1994	0.998390018939972
1995	0.987169981002808
1996	0.979120016098022
1997	0.975359976291656
1998	0.972180008888245
1999	0.971029996871948
2000	0.972530007362366
2001	0.974650025367737
2002	0.98199999332428
2003	0.984539985656738
2004	0.987110018730164
2005	0.989570021629334
2006	0.986199975013733
2007	0.987929999828339
2008	0.994979977607727
2009	0.998669981956482
2010	0.996879994869232
2011	0.995130002498627
2012	0.991649985313416
2013	0.991360008716583
2014	0.992529988288879
2015	0.989920020103455
2016	0.989430010318756
2017	0.993889987468719
2018	0.99440997838974
2019	0.992929995059967
2020	0.994620025157928