Year	Percent
1960	21.41581
1961	21.77991
1962	23.58937
1963	22.87759
1964	25.26187
1965	23.46952
1966	25.13292
1967	25.44509
1968	28.39839
1969	27.14268
1970	28.21979
1971	27.25235
1972	30.66895
1973	31.1206
1974	33.53057
1975	30.06201
1976	28.90895
1977	30.86891
1978	28.18119
1979	26.92283
1980	26.47788
1981	43.26836
1982	45.0839
1983	29.92263
1984	29.00422
1985	27.12023
1986	27.0258
1987	26.6787
1988	29.34848
1989	30.26984
1990	30.21886
1991	33.53321
1992	35.42841
1993	36.20941
1994	36.07097
1995	38.34488
1996	40.2191
1997	41.81635
1998	44.17866
1999	42.73547
2000	43.11444
2001	40.66846
2002	39.40046
2003	40.85088
2004	42.39362
2005	43.66581
2006	43.53023
2007	40.79568
2008	39.04582
2009	34.84007
2010	33.17296
2011	32.85658
2012	32.16957
2013	31.33302
2014	32.25501
2015	30.82495
2016	32.7909
2017	34.15226