Year	Percent
1977	11.29
1978	12.29
1979	14.93
1980	17.72
1981	14.78
1982	16.83
1983	10.21
1984	11.03
1989	10.93
1990	17.89
1991	21.22
1992	17.18
1993	22.53
1994	22.97
1995	23.91
1997	19.8
1998	19.79
1999	19.26
2000	22.73
2001	22.06
2002	23.81
2003	23.31
2004	24.26
2005	24.3
2006	23.94
2007	18.42
2008	18.8756
2009	22.3795
2010	22.1123
2011	22.441
2012	24.0122
2013	24.1659
2014	23.9966
2015	24.8138
2016	23.576
2017	23.06