Year	Percent
1960	22.40035
1961	21.44423
1962	19.9554
1963	25.54799
1964	28.22493
1965	31.17921
1966	31.13396
1967	30.63089
1968	29.59888
1969	29.47651
1970	30.17332
1971	29.21151
1972	31.00271
1973	33.75214
1974	40.25273
1975	37.1974
1976	36.63459
1977	40.3746
1978	39.1248
1979	39.77255
1980	39.57506
1981	33.8542
1982	28.77137
1983	25.24862
1984	25.42767
1985	22.95906
1986	27.69649
1987	34.35718
1988	32.88868
1989	32.83903
1990	36.75757
1991	32.45767
1992	36.64455
1993	34.55281
1994	33.13504
1995	37.16697
1996	33.02742
1997	34.82275
1998	37.29223
1999	37.01174
2000	38.81502
2001	43.16465
2002	56.89507
2003	57.42526
2004	60.54969
2005	58.35659
2006	59.34145
2007	60.01652
2008	56.93835
2009	49.67669
2010	53.94668
2011	56.68658
2012	53.53032
2013	51.14607
2014	49.53023
2015	44.40704
2016	40.00233
2017	38.86573