Year	Percent
1971	25.81071
1972	27.17801
1973	25.90311
1974	25.43277
1975	27.47629
1976	26.50038
1977	21.38881
1978	28.15026
1979	27.93561
1980	30.03843
1981	29.1188
1982	32.0608
1983	35.51583
1984	41.81818
1985	44.22457
1986	47.38594
1987	52.10673
1989	44.36114
1992	41.75753
1993	39.62847
1994	38.56108
1995	41.05307
1996	48.31117
1997	46.73102
1999	71.33139
2000	71.79012
2001	73.83786
2002	72.04242
2003	75.46589
2004	74.2766
2005	71.24858
2006	69.24467
2007	76.22982
2008	81.51089
2010	72.88599
2011	68.33139
2012	69.19349
2013	69.1956
2014	69.08812
2015	68.87775
2016	70.22551