Year	Percent
1960	13.33051
1961	12.29753
1962	11.37416
1963	10.61343
1964	13.49394
1965	19.20732
1966	14.36314
1967	14.98234
1968	12.42105
1969	19.53195
1970	27.5562
1971	27.58811
1972	27.61605
1973	26.88109
1974	27.89132
1975	31.01085
1976	31.8238
1977	32.46548
1978	37.41691
1979	42.72673
1980	43.89061
1981	40.98497
1982	43.29458
1983	47.73107
1984	51.62782
1985	56.75523
1986	57.93878
1987	58.02546
1988	61.91323
1989	61.42302
1990	56.90656
1991	53.54515
1992	49.66163
1993	47.8795
1994	43.25906
1995	43.89288
1996	45.4269
1997	45.69452
1998	43.54525
1999	44.80155
2000	46.30065
2001	44.76781
2002	43.96531
2003	39.61641
2004	38.82188
2005	42.85495
2006	43.59083
2007	41.80013
2008	36.54051
2009	28.15606
2010	31.8613
2011	34.30697
2012	29.18147
2013	31.4827
2014	33.07618
2015	29.98052
2016	32.09036
2017	30.2585