Year	Percent
1965	17.69374
1966	18.42553
1967	15.24823
1968	21.55689
1969	18.79006
1970	17.55692
1971	16.35012
1972	18.46591
1973	22.25089
1974	16.25616
1975	20.76164
1976	19.40772
1977	19.8146
1978	20.17853
1979	21.64885
1980	21.95227
1981	24.70491
1982	25.52276
1983	24.07926
1984	25.02487
1985	22.07489
1986	22.99504
1987	22.94502
1988	21.01249
1989	22.88737
1990	23.41547
1991	21.71062
1992	23.80461
1993	23.55908
1994	24.67525
1995	24.65662
1996	22.04498
1997	22.38119
1998	22.25065
1999	21.8239
2000	21.94715
2001	22.14312
2002	23.32352
2003	23.57617
2004	25.43446
2005	24.92223
2006	25.41722
2007	28.16044
2008	30.32118
2009	28.5377
2010	26.88479
2011	27.32041
2012	26.41186
2013	26.11928
2014	26.19705
2015	26.12258
2016	25.50638
2017	25.42973