Year	Percent
1981	29.32
1985	27.87
1990	29.97
1991	29.55
1992	33.91
1993	36.34
1994	34.86
1995	33.61
1996	38.76
1997	35.68
1998	33.4
2002	27
2003	26.55
2004	30.22
2005	25.91
2006	38.38
2007	38.67
2008	31.58
2009	39.55
2010	40.4
2012	42.93
2013	44.09
2014	45.04
2015	45.23
2016	46.51
2017	45.52