Year	% of total
1971	74.3103095893073
1972	75.65441696682389
1973	79.33357806658142
1974	75.03327431681831
1975	75.12567923593684
1976	75.74904036693613
1977	78.67152750354056
1978	77.3415193623175
1979	75.37842324238373
1980	73.55214887760751
1981	72.43961386422674
1982	70.77797618047818
1983	69.41132574517769
1984	69.6044901234621
1985	67.49558479619947
1986	67.15998752432928
1987	67.50496329125876
1988	68.6598160224781
1989	69.27715658370583
1990	65.681099850435
1991	66.91292172721751
1992	68.37345317254464
1993	68.4166684565963
1994	68.78671035732833
1995	68.52083383296427
1996	69.61284303231773
1997	70.58020567246017
1998	70.09029060731764
1999	71.46273814375928
2000	72.3911105148059
2001	72.50304598535662
2002	73.98245201125786
2003	76.12526643882694
2004	75.34972437497437
2005	75.54092621937555
2006	76.32278363704322
2007	77.78970380212508
2008	76.49935545621848
2009	76.5034376252809
2010	76.19990247459005
2011	79.02630445833674
2012	78.01849246603393
2013	77.81556880400757
2014	76.00942400144612
2015	74.56624231069246