Year	Percent
1960	45.55325
1961	38.28285
1962	41.58391
1963	42.35521
1964	38.51657
1965	34.95682
1966	33.86196
1967	35.86283
1968	39.39075
1969	41.15929
1970	43.24888
1971	43.85198
1972	36.79214
1973	37.59029
1974	41.10034
1975	41.62935
1976	34.14903
1977	33.68453
1978	33.54539
1979	36.77124
1980	35.47349
1981	36.07848
1982	36.88643
1983	37.51573
1984	38.04061
1985	40.06523
1986	34.72422
1987	35.31043
1988	32.64605
1989	31.2706
1990	32.33341
1991	32.53197
1992	30.37585
1993	29.60884
1994	30.61374
1995	31.91336
1996	35.6762
1997	35.17052
1998	38.34407
1999	37.24452
2000	39.4463
2001	38.24971
2002	34.33467
2003	35.93198
2004	38.0115
2005	42.49935
2006	48.28247
2007	42.48331
2008	43.38671
2009	40.50816
2010	43.28709
2011	48.41805
2012	50.73915
2013	47.2429
2014	46.66593
2015	45.85541
2016	42.04192
2017	42.84878