Year	Percent
1980	59.08816
1981	57.8035
1982	52.88151
1983	48.1914
1984	49.00919
1985	48.45241
1986	43.52361
1987	44.02584
1988	42.01837
1989	42.48869
1990	45.73458
1991	39.86438
1992	37.2115
1993	37.94498
1994	37.42497
1995	39.94764
2007	45.91787
2008	50.40782
2009	43.10005
2010	44.97605
2011	49.5171
2012	47.54907
2013	47.94526
2014	46.51985
2015	40.29848
2016	39.42624
2017	41.45492