Year	Percent
1965	14.63414
1966	20.36082
1967	22.58065
1968	23.80208
1969	24.75309
1970	23.34051
1971	23.97659
1972	24.29088
1973	23.32746
1974	22.29309
1975	21.31809
1976	19.01615
1977	18.37396
1978	20.90279
1979	21.6009
1980	18.88361
1981	17.79661
1982	12.34241
1983	13.87648
1984	13.99354
1985	14.62585
1986	12.63332
1987	14.50482
1988	15.88277
1989	18.04112
1990	18.70161
1991	19.90596
1992	19.74751
1993	20.69411
1994	20.96679
1995	20.10903
1996	16.17437
1997	13.70578
1998	13.36434
1999	13.47797
2000	13.89835
2001	13.69266
2002	13.27262
2003	13.0567
2004	13.32134
2005	13.55852
2006	13.57958
2007	13.55602
2008	12.6104
2009	12.81383
2010	12.81003
2011	13.13551
2012	12.98382
2013	15.93068
2014	16.02349
2015	15.51485
2016	15.14483
2017	15.41628