Year	Percent
1972	14.55843
1973	14.79492
1974	15.07836
1975	16.57197
1976	15.99797
1977	16.72721
1978	15.93752
1979	16.04372
1980	16.99699
1981	17.88451
1982	18.92269
1983	18.77016
1984	17.67541
1985	15.67709
1986	12.74774
1987	13.09159
1988	14.09103
1989	15.70942
1990	14.54317
1991	15.17877
1992	16.09528
1993	16.2793
1994	16.59357
1995	15.75433
1996	15.87958
1997	15.30626
1998	14.03441
1999	14.53198
2000	14.89308
2001	14.66862
2002	12.77107
2003	12.52871
2004	11.69058
2005	11.61246
2006	11.89772
2007	12.88886
2008	13.85357
2009	13.07234
2010	12.96903
2011	13.26644
2012	13.78688
2013	13.40734
2014	13.70066
2015	13.30857
2016	13.70826