Year	Percent
1982	22
1983	20.9
1984	21.1
1985	21.6
1986	21.7
1987	21.5
1988	21.4
1989	22.6
1990	23.6
1991	24.5
1992	26.3
1993	27.7
1994	30
1995	35.6
1996	38.8
1997	36
1998	34.5
1999	32.4
2000	32.2
2001	30.52
2002	31.94
2003	36.69
2004	37.16
2005	37.25
2006	36.03
2007	34.93
2008	33.76
2009	32.18
2010	32.02
2011	31.38
2012	31.02
2013	29
2014	28.03
2015	26.07
2016	23.72
2017	22.38
2018	20.74
2019	17.26
2020	17.2