Year	Percent
1972	7.61062
1973	7.09117
1974	8
1975	9.18182
1976	9.04449
1977	9.95133
1978	10.74027
1979	11.34289
1980	12.05817
1981	11.13106
1982	11.9208
1983	13.63611
1984	13.24353
1985	13.0299
1986	12.33332
1987	13.40896
1988	11.31646
1989	12.05339
1990	11.78268
1991	11.54614
1992	11.58803
1993	9.07061
1994	8.49192
1995	8.47962
1996	8.74298
1997	8.98773
1998	8.15561
1999	8.60814
2000	9.57286
2008	10.02377
2009	9.6798
2010	10.11091
2011	10.0124
2012	9.77302
2013	10.29458
2014	10.63341
2015	12.80693
2016	13.5542