Year	Percent
1972	14.99684
1973	16.62126
1974	11.39925
1975	8.47622
1976	13.37259
1977	16.98043
1978	15.518
1979	16.49189
1980	18.51357
1981	17.23483
1982	17.45172
1983	16.40634
1984	19.85113
1985	15.8943
1986	15.73434
1987	15.56505
1988	16.29858
1989	17.21579
1990	16.73822
1991	16.47744
1992	18.38602
1993	19.71567
1994	22.31655
1995	26.87155
1996	24.29235
1997	25.07031
1998	25.23979
1999	26.97064
2000	28.61544
2001	27.96377
2002	26.93695
2003	28.96328
2004	31.24168
2005	33.38856
2006	38.75883
2007	39.00071
2008	42.81246
2009	36.02324
2010	40.78416
2011	47.15024
2012	44.46765
2013	44.13522
2014	41.37061
2015	38.15176
2016	36.0077
2017	35.55969