Year	Percent
1973	22.751
1974	21.49055
1975	22.62548
1976	22.59269
1977	23.69738
1978	23.48951
1979	23.41892
1980	23.37312
1981	22.18729
1982	21.96628
1983	21.05481
1984	20.41832
1985	20.60523
1986	21.53348
1987	22.82658
1988	22.90137
1989	22.17643
1990	23.58726
1991	24.80774
1992	23.94208
1993	24.63042
1994	22.12919
1995	21.10217
1996	21.67384
1997	21.26994
1998	21.02822
1999	21.4274
2000	21.19868
2001	21.53616
2002	21.39975
2003	20.56798
2004	20.39207
2005	21.41534
2006	21.77545
2007	21.9306
2008	21.37499
2009	20.9771
2010	21.34528
2011	20.39868
2012	19.60819
2013	19.92637
2014	20.872
2015	21.45314
2016	22.17662