Year	Percent
1977	10.84709
1978	10.51535
1979	11.19902
1980	10.20014
1981	11.69602
1982	13.72169
1983	13.02044
1984	12.49234
1985	12.84751
1986	13.36652
1987	14.1746
1988	14.41888
1989	13.44156
1990	13.30159
1991	15.32376
1992	15.27374
1993	14.88676
1994	15.4584
1995	15.85036
1996	15.55657
1997	16.1701
1998	16.64912
1999	17.3664
2000	17.90944
2001	16.51186
2002	16.61716
2003	17.00871
2004	16.71183
2005	22.85394
2006	19.42265
2007	18.81854
2008	17.55444
2009	14.72582
2010	14.70952
2011	13.34308
2012	12.31799
2013	13.39788
2014	12.81064
2015	12.3244
2016	12.2001
2017	13.2166