Year	Percent
1971	26.44061
1972	30.65407
1973	31.23372
1974	29.84651
1975	37.37687
1976	35.89976
1977	35.41597
1978	37.79687
1979	38.9861
1980	40.20206
1981	43.84053
1982	45.76844
1983	52.55805
1984	41.2682
1985	47.30083
1986	43.07334
1987	41.56422
1988	37.868
1989	37.31694
1990	26.1173
1991	29.07171
1992	29.67355
1993	32.60429
1994	35.07749
1995	40.89116
1996	44.24031
1997	47.29683
1998	50.8066
2000	49.37075
2001	54.06932
2002	56.63006
2003	60.79333
2004	63.06276
2008	73.5933
2010	75.01156
2011	79.10286
2012	80.35019
2013	85.47702
2014	85.20401
2015	86.04279