Year	Percent
1972	16.22327
1973	17.4205
1974	16.33795
1975	20.60115
1976	18.39775
1977	18.75577
1978	18.68081
1979	17.94536
1980	19.04662
1981	20.12059
1982	19.7535
1983	18.84345
1984	20.02819
1985	18.13121
1986	17.9795
1987	16.80832
1988	14.37403
1989	13.94036
1990	13.30738
1991	15.22796
1992	15.74289
1993	16.31459
1994	15.62474
1995	15.10075
1996	16.17061
1997	15.92535
1998	15.85208
1999	15.17976
2000	16.15269
2001	16.03355
2002	16.2017
2003	15.94896
2004	16.40223
2005	18.02512
2006	19.49191
2007	20.25693
2008	18.71186
2009	14.5231
2010	17.35651
2011	18.85899
2012	18.99487
2013	17.38697
2014	16.96739
2015	17.43801
2016	17.41744