Year	% gross
1970	13.212420463562
1971	13.2251396179199
1972	13.4219598770142
1973	13.7134895324707
1974	13.6709499359131
1975	13.8983697891235
1976	13.9499502182007
1977	14.3394403457642
1978	14.8426399230957
1979	15.5499801635742
1980	16.5305500030518
1981	16.1911602020264
1982	16.9662704467773
1983	17.6960105895996
1984	17.9543991088867
1985	17.7505493164062
1986	17.6532001495361
1987	17.8474502563477
1988	18.0382595062256
1989	18.1382808685303
1990	17.7988700866699
1991	18.791259765625
1992	19.5468006134033
1993	20.3007907867432
1994	21.3161506652832
1995	22.6175594329834
1996	23.474910736084
1997	24.1961898803711
1998	25.336950302124
1999	26.3075904846191
2000	27.3625793457031
2001	28.520580291748
2002	29.6193695068359
2003	30.145149230957
2004	30.5865097045898
2005	31.2397804260254
2006	32.5666084289551
2007	33.5522499084473
2008	34.8448715209961
2009	36.6938705444336
2010	38.2853698730469
2011	39.2785110473633
2012	40.7266387939453
2013	42.3115692138672
2014	43.2845306396484
2015	43.9193305969238
2016	45.3731384277344
2017	45.4377784729004
2018	46.2577705383301
2019	46.1748085021973
2020	46.6212615966797
2021	46.4645500183105