Year	Percent
1970	21.66071
1971	22.06009
1972	23.82426
1973	23.59791
1974	20.43517
1975	22.86633
1976	26.66762
1977	26.10583
1978	26.52442
1979	28.83773
1980	28.92279
1981	28.21414
1982	27.52947
1983	28.20712
1984	31.46482
1985	28.98583
1986	26.6371
1987	26.14667
1988	26.01093
1989	26.20084
1990	26.7478
1991	29.15405
1992	31.20203
1993	30.64409
1994	30.86775
1995	29.39367
1996	28.34888
1997	28.32064
1998	29.61704
1999	30.95055
2000	35.74576
2001	35.43104
2002	32.84707
2003	29.83973
2004	29.5436
2005	28.28551
2006	29.59003
2007	29.24601
2008	32.04301
2009	28.74219
2010	30.25994
2011	30.36424
2012	28.86165
2013	28.8001
2014	27.88084
2015	27.57475
2016	25.81772