Year	Percent
1960	40.31563
1961	41.34002
1962	39.54972
1963	40.12237
1964	40.23828
1965	42.80021
1966	40.6468
1967	41.06314
1968	42.27014
1969	42.51128
1970	42.47721
1971	43.30384
1972	40.63121
1973	39.36809
1974	38.88564
1975	40.28328
1976	38.24229
1977	35.34061
1978	37.34543
1979	39.74766
1980	39.6995
1981	40.50245
1982	40.54219
1983	40.50824
1984	40.92978
1985	42.41893
1986	42.13461
1987	43.02867
1988	43.15347
1989	43.68093
1990	44.11669
1991	45.10011
1992	45.60127
1993	43.86652
1994	41.71
1995	44.72917
1996	45.55348
1997	45.98858
1998	45.54928
1999	45.10117
2000	45.00851
2001	45.73097
2002	47.44435
2003	47.46418
2004	47.76373
2005	47.85937
2006	50.35668
2007	50.22765
2008	50.12477
2009	49.31683
2010	48.10602
2011	47.07766
2012	47.80114
2013	48.00803
2014	47.97578
2015	46.21641
2016	44.7406
2017	45.37852