Year	Percent
1980	31.46561
1981	31.11182
1982	30.57021
1983	25.97843
1984	19.2678
1985	13.25679
1986	15.23285
1987	20.56118
1988	23.94587
1989	22.39454
1990	16.91503
1991	16.44737
1992	17.97302
1993	13.48854
1994	15.56576
1995	14.20074
1996	15.05518
1997	15.83302
1998	19.61137
1999	19.80752
2000	20.24493
2001	21.83618
2002	17.35291
2003	19.42174
2004	20.37289
2005	19.11393
2006	20.35455
2007	20.09151
2008	18.03185
2009	17.65698
2010	17.55023
2011	17.75245
2012	17.42975
2013	16.97512
2014	18.76544
2015	19.64522
2016	19.685
2017	17.63511