Year	Percent
1960	29.62966
1961	29.35487
1962	32.40744
1963	29.91459
1964	31.94109
1965	34.42264
1966	34.08664
1967	32.45614
1968	33.55592
1969	35.77577
1970	45.15664
1971	45.7541
1972	48.93619
1973	47.79248
1974	42.25352
1975	46.86319
1976	47.22973
1977	45.07854
1978	53.11828
1979	49.39377
1980	47.73011
1981	49.33078
1982	49.66666
1983	44.10555
1984	46.33524
1985	44.67154
1986	45.37289
1987	46.53703
1988	44.876
1989	43.45771
1990	43.71738
1991	42.02026
1992	40.9637
1993	35.17954
1994	43.84945
1995	40.05642
1996	38.10241
1997	37.68434
1998	48.17484
1999	46.85697
2000	46.53952
2001	45.12685
2002	43.4155
2003	45.79319
2004	46.61994
2005	43.40176
2006	45.69318
2007	45.48725
2008	41.11827
2009	51.10462
2010	52.79335
2011	51.60937
2012	29.87817
2013	32.6614
2014	31.62876
2015	31.26757
2016	30.8297
2017	29.78384