Year	Percent
1960	23.24783
1961	23.00533
1962	23.41637
1963	23.42681
1964	23.3994
1965	23.77029
1966	23.70868
1967	23.70425
1968	24.30917
1969	26.848
1970	27.39176
1971	27.03535
1972	26.93067
1973	26.91937
1974	29.11437
1975	28.09464
1976	28.75253
1977	27.95396
1978	29.11509
1979	30.88078
1980	31.69307
1981	33.00066
1982	31.7415
1983	30.4782
1984	32.75102
1985	34.92132
1986	31.99771
1987	31.4062
1988	33.07093
1989	35.0152
1990	35.69741
1991	34.59049
1992	33.15527
1993	31.4639
1994	32.15853
1995	33.53314
1996	34.24928
1997	37.02808
1998	38.35102
1999	39.35704
2000	43.34627
2001	44.61756
2002	45.31939
2003	44.57041
2004	46.86721
2005	48.61975
2006	50.84167
2007	52.56087
2008	53.24886
2009	45.20742
2010	51.26216
2011	53.94867
2012	53.97368
2013	53.44129
2014	53.39945
2015	52.93149
2016	52.26183
2017	53.93638