Year	Percent
1980	70.01843
1981	56.15773
1982	52.12732
1983	44.83709
1984	45.15056
1985	51.37507
1986	56.28483
1987	46.26113
1988	46.04545
1989	49.63055
1990	43.33625
1991	43.76554
1992	42.78052
1993	47.0779
1994	44.46767
1995	45.09705
1996	45.9095
1997	43.1897
1998	41.87344
1999	41.96833
2000	40.87775
2001	41.17806
2002	46.00316
2003	43.38681
2004	39.81204
2005	40.44947
2006	45.4683
2007	50.48234
2008	54.35427
2009	52.34676
2010	47.75728
2011	45.52616
2012	43.41161
2013	41.18507
2014	38.71407
2015	38.39224
2016	41.13809
2017	36.67571