Year	Percent
1982	26.41
1983	26.95
1984	27.15
1985	28.65
1986	26.51
1987	25.71
1988	25.39
1989	27.55
1990	27.61
1991	26.29
1992	26.93
1993	25.76
1994	26.93
1995	16.69
1996	21.96
1997	18.59
1998	18.22
1999	18.13
2000	16.93
2001	16.93
2002	15.56
2003	15.99
2004	16.64
2005	15.78
2006	16.87
2007	18.25
2008	19.05
2009	17.65
2010	19.18
2011	17.8
2012	16.88
2013	17.46
2014	19.12
2015	19.74
2016	19.41
2017	20.04