Year	Percent
1960	27.43121
1961	26.30875
1962	36.42629
1963	34.25755
1964	35.58242
1965	34.58872
1966	33.56784
1967	32.9603
1968	42.14116
1969	44.69602
1970	40.56536
1971	49.49918
1972	41.2723
1973	50.24842
1974	44.45873
1975	51.7011
1976	53.26393
1977	51.07136
1978	67.33097
1979	61.02106
1980	63.43313
1981	62.20496
1982	53.58287
1983	47.24023
1984	53.60832
1985	59.77029
1986	52.69407
1987	55.6874
1988	49.46208
1989	50.95884
1990	48.94808
1991	45.5633
1992	44.16752
1993	49.30311
1994	48.80361
1995	48.45768
1996	47.50025
1997	46.44503
1998	45.12446
1999	50.31149
2000	52.20671
2001	49.34504
2002	53.57589
2003	53.66895
2004	60.1588
2005	63.11249
2006	63.08043
2007	63.30484
2008	59.76328
2009	46.86785
2010	51.20597
2011	54.89704
2012	53.84158
2013	48.36709
2014	46.68686
2015	43.0268
2016	40.68651
2017	37.90762