Year	Percent
1969	17.58
1972	23.18
1973	22.11
1974	20.5
1975	19.65
1976	21.81
1978	23.72
1980	35.51
1981	25
1982	26.7
1985	33.39
1988	23.03
1990	15.72
1991	15.74
1992	15.75
1993	16.32
1994	15.34
1995	16.23
1996	16.01
1997	16.35
1998	15.5
1999	15.74
2000	15.54
2001	14.93
2002	14.19
2003	11.73
2004	12.21
2005	11.26
2006	10.32
2007	9.75
2008	10.59
2009	11.36
2010	12.37
2011	12.7
2012	13.93
2013	15.25
2014	13.74
2015	13.51
2016	13.19
2017	11.63
2018	9.1
2019	7.69