Year	Percent
1978	40.64563
1979	43.14888
1980	36.43132
1981	40.92794
1982	46.66667
1983	47.85714
1984	45.94595
1985	47.83648
1986	46.98266
1987	43.01211
1988	41.55287
1989	47.11552
1990	50.27236
1991	51.93322
1992	52.99643
1993	53.5212
1994	54.13478
1995	53.48464
1996	52.7085
1997	53.46704
1998	53.74962
1999	55.38841
2000	54.28092
2001	55.54735
2002	56.21418
2003	61.30607
2004	61.25788
2005	62.37623
2006	60.17343
2007	61.01241
2008	60.5898
2009	61.9816
2010	60.84234
2011	59.96868
2012	60.29952
2013	60.06088
2014	59.94212
2015	60.78612
2016	62.37537
2017	58.37867