Year	Percent
1976	20.037
1977	19.6327
1978	17.65513
1979	16.43227
1980	18.33736
1981	17.56847
1982	16.59043
1983	19.01047
1984	19.43576
1985	17.93524
1986	17.7038
1987	17.73821
1988	19.18551
1989	20.0091
1990	19.64681
1991	20.29344
1992	19.15029
1993	18.10063
1994	18.28151
1995	16.11422
1996	14.81299
1997	15.99348
1998	15.99336
1999	16.95371
2000	17.25244
2001	15.3981
2002	15.23951
2003	16.68844
2004	16.73149
2005	17.81921
2006	16.02867
2007	15.10546
2008	16.96722
2009	18.07301
2010	18.01671
2011	18.00452
2012	18.62171
2013	18.36661
2014	18.46619
2015	8.99396
2016	18.12841