Year	Percent
1980	48.34957
1981	40.10891
1982	36.67533
1983	34.70032
1984	32.57035
1985	37.21051
1986	35.56891
1987	30.39466
1988	33.2118
1989	33.72547
1990	29.01005
1991	25.95033
1992	25.29969
1993	22.92693
1994	24.4065
1995	21.95424
1996	21.43364
1997	22.07662
1998	22.95376
1999	21.62986
2000	25.46407
2001	28.53537
2002	29.54361
2003	26.44208
2004	27.00291
2005	26.7367
2006	31.99022
2007	32.21295
2008	34.63717
2009	29.12275
2010	27.91758
2011	27.80883
2012	30.03919
2013	29.9742
2014	29.21535
2015	28.53892
2016	29.30281
2017	28.44499