Year	Percent
1970	23.6481
1971	25.0112
1972	22.45342
1973	20.98052
1974	24.83648
1975	43.19649
1976	48.83319
1977	82.56653
1978	90.63161
1979	87.26565
1980	89.176
1981	101.55218
1982	114.76477
1983	115.05712
1984	112.62279
1985	115.02609
1986	124.39763
1987	110.41727
1988	132.47291
1989	116.70285
1990	78.56163
1991	89.06362
1992	75.05052
1993	66.62368
1994	62.76875
1995	55.5144
1996	46.22774
1997	37.72224
1998	37.5363
1999	33.88733
2000	28.97205
2001	28.66907
2002	33.69343
2003	36.73332
2004	39.88023
2005	34.14674
2006	28.6857
2007	26.24367
2008	20.6439
2009	18.72504
2010	17.16983
2011	15.32339
2012	14.40563
2013	16.19902
2014	13.73668
2015	14.59952
2016	20.01958