Year	Percent
1978	22.78063
1979	19.99341
1980	26.98331
1981	24.20943
1982	21.31102
1983	21.37566
1984	23.77904
1985	21.85035
1986	21.15427
1987	23.91973
1988	24.00762
1989	23.47515
1990	19.29548
1991	18.94629
1992	18.38363
1993	18.52679
1994	17.31954
1995	17.44308
1996	17.65751
1997	16.96306
1998	16.80069
1999	16.25093
2000	18.5363
2001	17.76392
2002	16.96371
2003	15.05507
2004	15.22025
2005	14.96977
2006	17.57495
2007	18.1311
2008	19.25585
2009	18.83576
2010	18.83138
2011	19.6985
2012	17.5594
2013	16.59985
2014	16.17901
2015	14.16829
2016	14.08165
2017	14.30903