Year	Percent
1970	28.49185
1971	27.85971
1972	27.40912
1973	23.08312
1974	22.0299
1975	15.11889
1976	13.69502
1977	11.30328
1978	12.10097
1979	14.85114
1980	16.59514
1981	22.83447
1982	30.45947
1983	39.54748
1984	30.91486
1985	43.06068
1986	34.07517
1987	40.08243
1988	47.5971
1989	51.71377
1990	43.10676
1991	39.80865
1992	41.38441
1993	35.41843
1994	49.14561
1995	33.69889
1996	39.10515
1997	29.94977
1998	31.62154
1999	44.58382
2000	30.49105
2001	39.62059
2002	45.76286
2003	53.04171
2004	37.90347
2005	39.77106
2006	33.9645
2007	23.5665
2008	17.69709
2009	21.96712
2010	20.54586
2011	15.35948
2012	21.19716
2013	14.00211
2014	21.82198
2015	27.79455
2016	28.93805