Year	Percent
1972	22.95168
1973	20.68992
1974	20.4623
1975	20.38592
1976	21.53183
1977	22.08057
1978	21.81944
1979	22.2387
1980	25.11382
1981	26.2503
1982	25.31305
1983	24.55872
1984	24.53237
1985	25.6546
1986	25.62118
1987	23.62812
1988	22.15428
1989	20.47768
1990	21.30451
1991	21.5761
1992	20.7365
1993	20.7365
1994	21.74283
1995	23.46904
1996	24.44766
1997	24.29678
1998	24.13428
1999	24.36452
2000	26.78936
2001	26.12942
2002	27.12845
2003	25.86408
2004	27.32437
2005	28.19891
2006	28.89692
2007	28.11028
2008	27.86565
2009	25.88094
2010	26.8212
2011	27.67624
2012	26.96184
2013	25.07716
2014	23.46596
2015	22.08936
2016	21.99384