Year	Percent
1980	29.20354
1981	25.20325
1982	26.15385
1983	31.06061
1984	32.62411
1985	34.04255
1986	29.92701
1987	28.87324
1988	30.61224
1989	27.77778
1990	30.66667
1991	28.125
1992	23.39142
1993	5.99991
1994	2.64657
1995	4.0329
1996	19.59586
1997	17.83735
1998	27.17044
1999	26.45302
2000	26.58151
2001	30.32776
2002	28.50108
2003	31.32071
2004	31.90818
2005	33.48725
2006	30.85814
2007	32.05591
2008	25.95885
2009	13.02606
2010	21.58611
2011	26.15843
2012	28.94986
2013	24.78051
2014	29.80689
2015	31.50418
2016	32.72722
2017	31.89432