Year	Percent
1960	26.74533
1961	28.64329
1962	28.85281
1963	28.28333
1964	28.29879
1965	27.01668
1966	26.76578
1967	26.13048
1968	26.71442
1969	28.72806
1980	49.29035
1981	48.38306
1982	44.33942
1983	44.63659
1984	45.02222
1985	45.72792
1986	43.63845
1987	40.30958
1988	41.51619
1989	44.08178
1990	41.59233
1991	38.74894
1992	38.42152
1993	37.04925
1994	36.24914
1995	36.41365
1996	37.92931
1997	42.13131
1998	42.16449
1999	42.66281
2000	45.98769
2001	45.27436
2002	42.21605
2003	41.42146
2004	42.52151
2005	46.53934
2006	48.02667
2007	50.00721
2008	52.11823
2009	49.69971
2010	53.28651
2011	57.03067
2012	56.64875
2013	59.87161
2014	52.5864
2015	50.62988
2016	54.5889
2017	53.92747