Year	Percent
1960	15.9026
1961	14.98488
1962	16.65485
1963	15.92152
1964	16.1168
1965	18.09182
1966	18.5892
1967	15.92068
1968	14.5713
1969	16.30531
1970	16.87829
1971	17.84252
1972	16.35411
1973	19.3157
1974	19.50388
1975	19.21382
1976	19.41213
1977	19.87891
1978	23.56147
1979	22.73416
1980	21.36261
1981	21.11165
1982	21.26553
1983	20.31922
1984	21.31469
1985	22.96029
1986	22.37803
1987	24.37474
1988	25.4568
1989	26.42433
1990	29.01192
1991	24.29576
1992	25.67458
1993	24.72909
1994	27.55923
1995	28.16718
1996	26.39364
1997	28.499
1998	26.97642
1999	29.68224
2000	27.03988
2001	27.01881
2002	27.58306
2003	29.90266
2004	36.57486
2005	38.61619
2006	39.74021
2007	42.47625
2008	38.23139
2009	40.65597
2010	40.68155
2011	39.59042
2012	38.34742
2013	34.0232
2014	34.26781
2015	31.79231
2016	30.34734
2017	30.7476